From attending school in Wiltshire with one another to becoming flatmates in their 20s and later navigating motherhood together, Kate and Pippa Middleton have shared many big milestones.
They share a close sisterly bond and even as Kate has risen through the ranks of the royal family, sister Pippa is always by her side, stealing Kate's style secrets, taking in the tennis with her and just generally being a supportive presence.
From simpler times before titles and tiaras, we look back at some of the best moments between the Middleton women.
32 of Kate and Pippa Middleton's most iconic sister moments
Party girls
Let's be honest, we've seen Kate Middleton's best style moments over the years blossom to include tiaras and treasured heirlooms, so it's easy to forget that she was just a young girl living it up in London at one point.
Back in 2008, Kate, Pippa and their mutual friends hit the town in their finest Day-Glo fashions. No, they were not victim to a passing fad. The fancy dress attire was in honour of a Midnight Roller Disco throwing in aid of a charity set up to honour one of their friends, Thomas Waley-Cohen.
Watching the boys play Polo
Sisters sat outside in the sunshine, drinking wine al fresco and watching the boys play Polo. Sounds like quite the carefree summer.
Kate was joined by her sister as she cheered William on in 2009 - and it has to be said that Pippa is a most supportive sister joining Kate, as they both look terribly bored.
The man sat with them is Thomas van Straubenzee. Little did Kate at the time know he would become the godfather to her second child, Princess Charlotte!
Being hair goals at Wimbledon 2012
The Middleton clan all love a spot of tennis, and it must be one of Kate Middleton's proudest moments getting to share the royal box with the likes of Pippa, mum Carole, dad Michael and brother James.
The family attend every year, and during this appearance in 2012, it has to be pointed out that both Kate and Pippa are giving ultimate hair goals.
Kate's hair secret is reportedly a rather affordable brush, and we wonder if she's shared that little tip with Pippa.
Pre-wedding fun
On 29 April 2011, Kate would walk down the aisle of Westminster Abbey and marry Prince William, an heir to the throne. Daunting, to say the least.
But the night before, Kate had her sister by her side as they checked into the Goring Hotel - a five-star luxury hotel in Belgravia that has a long-standing connection to royalty - for one last night before their lives would change forever.
Sisters on the town
In 2007, Prince William and Kate Middleton actually split and took some months apart. Unthinkable, given what we know of their endearing, fairy-tale romance now.
But during those times in 2007, any heartaches Kate might have felt were soothed by her younger sister. The pair were spotted all around London during those days, glamming up and going to chic events like book launches.
Dressed in a lacy Collette Dinnigan bodycon dress, a young Kate looked happy and glowing at the launch of Young Stalin - not quite the go-to reading we imagined for the future Princess of Wales.
Stylish wedding guests
2011 was a busy year for weddings. Not only did Kate Middleton marry Prince William in April of that year, Zara Tindall and Mike Tindall got hitched in June and so did Sam Waley-Cohen, a Middleton family friend.
For this wedding, Kate and Pippa were the ultimate stylish siblings.
Kate wore a silky-effect black and white print monochrome dress from Zara and her hat was a most economical choice as she wore the same one that morning to Trooping the Colour. That's right - she had to dash from London for her first-ever Trooping the Colour ceremony to make it to the afternoon wedding.
Pippa brought a pop of colour with a silky olive green coat.
Whispering at Wimbledon
Oh, to overhear what the Middleton sisters whisper about.
The close sisters enjoyed another outing at Wimbledon in 2019, where they were captured having a little gossip session.
We have to give Kate props on her poker face, as she's revealing nothing, but it does look like Pippa is sharing something juicy.
This was a special sighting of the sisters for fans, as, per the Daily Mail, the pair hadn't made a public outing together since 2012.
Letting their guard down together
During Kate Middleton's single chapter in 2007, following a very short separation from Prince William, Pippa was right by her side for the ups and downs.
In this iconic moment, the pair were clearly enjoying a more light-hearted moment, as we see Kate making the sort of unguarded, candid facial expression that we don't see much of now she's mastered being the Princess of Wales.
Bonding with Meghan Markle
One sister by blood, and one by marriage. It was an iconic day out at Wimbledon 2019 when Kate and Pippa Middleton bonded with Kate's new sister-in-law, Meghan Markle.
They must have all hit it off, as Meghan would later get an invite to the reception for Pippa's wedding to James Matthews.
Touchingly, Meghan only showed up at the reception for a selfless reason - not to cause a media storm and upstage the bride. (This was during the earlier stages of Harry and Meghan's courtship in 2017).
"Right now Harry and Meghan are leaning towards not wanting to attract extra attention, especially on a day that's not about them," said a source who spoke to E! News.
Making an entrance, Wimbledon
All it took was the arrival of the Middleton sisters to steal centre stage from centre court at Wimbledon 2012.
The two sisters watched Britain's Andy Murray play Roger Federer in the men’s singles final - while it was a loss for the UK (Murray lost), Kate might not have too cut up - she and Federer have enjoyed a friendship over the years, with the former World Number One even giving Prince George a private lesson.
Both sporting impeccable Wimbledon looks, Kate's cream outfit pieces were from designer Joseph Vanessa. Pippa's blue and white pattern dress is from Project D.
Offering two takes on winter fashion
For the chilly Cheltenham races in March 2006, Kate and Pippa Middleton both offered their varying takes on winter fashion.
Pippa kept hers lowkey, wearing a timeless wool overcoat that complemented her black boots.
Kate, however, decided to go a bit more grand, giving off Russian aristocrat vibes with a huge fur hat. Kate's showstopping hat went perfectly with her creamy, neutral-coloured coat, from designer Katherine Hooker.
Even a taxi ride can be fun with your best friend/sister
Proving their sisterly bond - and giving us serious FOMO - the Middleton sisters make a taxi ride to the nightclub look like the most fun experience. Full of smiles - and what appears to be quite the fake tan on Pippa - it's a snapshot of late 2000s fashion, and a refreshing reminder that before her titles, Kate was just another young girl having fun in one of the best cities in the world.
The pair were heading to the charity Day-Glo roller disco in honour of a friend who had sadly passed from cancer.
Pippa joins Kate on the Buckingham Palace balcony
Sure, we're used to seeing siblings take centre stage throughout the most iconic Buckingham Palace balcony photos over the years. But they are siblings born and bred into royalty, from Princes Harry and William to Charles, Anne and more.
Standing on the instantly recognisable balcony of one of the most famous royal palaces across the globe must have been a surreal moment for the Middleton family and an undeniably iconic moment for the sisters.
The family were welcomed onto the balcony following the wedding of Prince William and Kate Middleton in April 2011.
Kate in big sister mode
Kate Middleton has some surprising hidden talents, but one which is well known is her skill for tennis.
This could explain why, during a Wimbledon appearance with her younger sister Pippa, Kate went into full big sister mode and appears to be pointing out all manner of things.
The full photo collection from this event shows Kate energetically pointing and talking away at Pippa who, to her credit, seems to just let her big sis get carried away sharing her love for the sport.
The Middletons go to church
If Prince William thought it was only his side of the family who could unite for an iconic Christmas day walkabout, he had another thing coming.
In 2016, Kate (carrying Princess Charlotte) joined her family for a sweet Christmas day outing in Bucklebury, Berkshire. Pippa and James, Kate's brother, looked pleased to have their sister join them for the festivities, and it marked one of the first Christmases that Kate and her brood spent it away from Sandringham.
Pippa shines with her own cookbook
Sometimes the best thing a sister can do is let her younger sibling have her moment. And that's what many predicted happened when Kate was notably absent from Pippa's book launch.
Pippa released her first cookbook, Celebrate: A Year of Festivities for Families and Friends, in 2012, and enjoyed several glitzy parties to commemorate.
Perhaps knowing an appearance from the newly married Kate would overshadow it, Kate supported privately. Still, it's an undeniably iconic achievement for Pippa and another feather in the cap for the accomplished sisters.
The Princess of Wales dotes on her sister for her big day
Not many people - if any! - can say that they had the future Queen doting on them on their wedding day. But that's exactly what happened during Pippa Middleton's enchanting Berkshire wedding to James Matthews in 2017.
Despite her titles, Kate's most important role on the day was being big sister, and she didn't hesitate in helping sort out Pippa's train before she took the walk down the aisle.
Curious about Pippa's gown? She got married wearing a bespoke lace gown with a high neck, cap sleeves and an open back by designer Giles Deacon.
Sibling support on the Coronation
Sadly there were no photos of the Middleton siblings together during the historic Coronation of King Charles in May 2023, but it must have been a relief for the Princess of Wales just to know she had some of her lifelong supporters there during the momentous day.
For the important day, Pippa looked stunning in a pastel yellow Claire Mischevani coat dress and matching fascinator.
Kate making sure Pippa's wedding went off without a hitch
When it comes to your only sister getting married, Kate Middleton proved that any sense of royal protocol or fancy title meant nothing.
Dressed in custom Alexander McQueen, Kate stepped up for her sister, even going as far as shushing the children to make sure no moments were ruined.
It's a sign of their bond that the future Queen would be reduced to dealing with rowdy Page Boys and flower girls for her sister's sake, and it's one of the defining moments of their relationship.
Putting Prince William through the sister test
Sure, you might be the heir to the throne but to paraphrase the Spice Girls, if you wanna be my lover, you gotta get with my friends - and sister. That's at least the hilarious vibe we're getting from these iconic photos of Prince William doing his best to win favour with Kate's younger sister in 2006.
Pippa joined her older sister to watch Prince William partake in some sports at his old alma mater, Eton.
Family support for Kate's Christmas Carol concert
In 2022, Kate Middleton hosted her first Together at Christmas carol concert since the coronavirus pandemic.
Supporting her sister's initiative, which also marked the first one since the death of Queen Elizabeth II, the Middleton's turned out in full force.
Pippa wore a wine-coloured long trench Karen Millen coat. She completed her winter-ready look with a large black statement belt, cinched securely around her waist.
Pippa sharing the spotlight at her wedding with a touching gesture
According to The Sun, Pippa Middleton honoured her big sister in a touching way during her 2017 wedding.
Kate reportedly showcased her artistic talents and drew a sketch of St. Marks's church, where the couple were married.
This drawing was featured on their order of service.
At the reception at the Middleton family home, Kate's brother-in-law praised the gesture, saying "And to Pippa's sister Kate, such ability - a beautiful drawing of St. Mark's church in the order of service."
Kate and Pippa - sisters and confidants
At Wimbledon, fans got to see a rare, candid side of Kate, enjoying a gossip with her sister and looking totally at ease.
It's no surprise that the two have remained close confidants.
Per The Mirror, in a previous interview with NBC, Pippa opened up about her close relationship with Kate, saying: "I mean, obviously she has pressures that she's taken on and things. But we spend a lot of time together. We still do a lot together as a family. We have a very normal, sisterly relationship. We're very close. And, you know, we support each other and get each other's opinions and things."
Country girls in their element
Fans have become used to Kate Middleton's dazzling tiara moments in recent years, but she will forever be a country girl at heart.
A fun fact about Kate's wedding to William was that her love for the bucolic country life almost meant defying tradition as she considered a flower crown instead of the Cartier Halo tiara.
This could explain why Kate and Pippa look so natural just walking around in their casual boots and rural attire.
Pippa charming Kate's (rather daunting) in-laws
Another iconic moment which sums up how the sisters are always a support to one another, even when not together, was Pippa's ease and confidence when mingling with her sister's incredibly famous in-laws.
Many might have buckled standing next to the likes of Queen Elizabeth II and Prince Philip, but Pippa had no issue chatting away as the world turned their gaze on the newly bonded family after the Royal Wedding in 2011.
Pippa supports Kate during a tough time
While they've never quite acknowledged it as such, 2023 could have been considered something of an Annus Horribilis for the Royal Family.
They lost their long-serving matriarch, Queen Elizabeth, in late 2022 and then William, Kate, King Charles and Queen Camilla in particular faced scrutiny following the release of Prince Harry's jaw-dropping memoir, Spare.
As they went about their business - upholding the royal mantra of 'never complain, never explain' - it's fair to assume that Kate having the support of her sister during her 2023 Carol Concert must have been more than welcome.
Commanding attention at Wimbledon
Walking to their seats in the royal box at Wimbledon, Kate and Pippa (joined by Meghan Markle) looked effortlessly stylish and iconic - and had most of the audience paying attention to the audience instead of the tennis court.
The sisters (and sister-in-law) joined forces to watch Serena Williams and Simona Halep play the Ladies' Singles Final at The Championships.
The Princess of Wales opted for an elegant long green Dolce and Gabbana dress which perfectly complemented her brunette locks.
Pippa rushes to her sister's side
In December 2012, Kate Middleton was admitted to the King Edward VII Hospital after suffering from acute morning sickness.
It must have been a worrying side for the family - Kate was the first Middleton sibling to be pregnant (with her first child, Prince George).
Pippa wasted no time in getting to her sister's side.
Pippa's stint as arguably the most famous Maid of Honour in history
The world tuned in in their billions - literally - to watch the 2011 wedding of Kate Middleton and Prince William. And while everyone expected all eyes to be on the bride - who would she wear? - Pippa Middleton almost became the unlikely spotlight-stealer.
Pippa's now legendary time in the spotlight came as a result of the Sarah Burton designed dress, which highlighted her derriere.
Seeing the funny side a few years later, Pippa joked about the attention she received. "As I have found out, recognition has its upside, its downside and - you may say - its backside," she cracked at a dinner for Women in Advertising and Communications in London, per Glamour.
Caring sisters honouring their mum on Kate's wedding day
The Middleton girls made sure to honour their own lineage during the historic Royal Wedding in 2011.
While a lot of traditions and protocol adhering to Prince William's royal roots had to be observed, Kate found a way to pay tribute to her mother, and Pippa was part of the touching gesture.
Kate's bridal party wore flower crowns modelled after the one her mother, Carole Middleton, wore at her own wedding in 1981.
Pippa's big day honoured her family
Pippa Middleton's 2017 wedding to James Matthews included some of the most touching signs of how close she remains with her sister, despite the pressures of her royal status.
Kate was all smiles as she carried out her big sister duties, including helping Pippa make her grand entrance in her bespoke Giles Deacon gown, holding up the train, and also leading the group of young children serving as bridesmaids and page boys.
While Kate wasn't officially a bridesmaid or Maid of Honour, Pippa chose Kate's children - Prince George and Princess Charlotte - to be in the bridal party. (Louis wasn't born until 2018!)
Kate and Pippa at the Royal Wedding, 2011
Forget the Kardashians and other famous sisters - no siblings could compete with the sheer magnitude of being there for each other during one of the most iconic royal weddings in modern history.
From their first appearance - when the world got its first look at Kate Middleton's elaborate, lacy Alexander McQueen dress - Pippa was the ultimate sidekick and support for her big sister.
