The annual Trooping the Colour parade is one of the major events of royal calendar - and this year it is set to be even more poignant.
Not only will the parade on Saturday be King Charles' first ever birthday parade, it will also be the first for the Princess of Wales in her new military role.
It was last year that she became the Colonel of the Irish Guards - a position previously held by her husband Prince William.
And already this year, she has fulfilled colonel duties, which have included taking part in the Irish Guards' well-known St Patrick's Day parade.
At Trooping the Colour, colonels usually wear full military uniform, with some, including William and Princess Anne, even taking part in the parade on horseback.
And even though it has been announced that both Charles and William will ride on horseback during the display - it is reported that Kate will not and instead travel to Horse Guards Parade in a carriage.
And according to the Daily Mail last year, Kate is also not expected to wear military uniform for the parade.
The same goes for Queen Camilla, who was recently appointed Colonel of the Grenadier Guards, a role previously held by Prince Andrew but has been vacant since he was stripped of his royal titles.
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She is also not expected to wear military uniform and will also ride in a carriage.
Trooping the Colour has marked the monarch's official birthday for over 260 years, and Saturday will mark Charles' first appearance at the event as King, and follows his Coronation, which was held.
Over 1,400 parading soldiers, 200 horses and 400 musicians take part in the display of military precision, horsemanship and fanfare.
The parade travels from Buckingham Palace down The Mall to Horse Guards Parade and closes with a Royal Air Force fly-past.
However, Kate has been seen in uniform several times in the past year on several different military engagements.
Last year, pictures showed Kate on a visit to Pirbright Training Academy, where she spent time with the 101 Operational Sustainment Brigade at Abingdon Airfield to see how new recruits and serving personnel are trained.
She also took part in some of the training exercises and spent time speaking to personnel about their experiences in the British Army.
In photos, Kate can be seen smiling as she's put to the test through a number of training exercises.
She can also be seen sitting in a tank as well as getting stuck in and lending a hand to help repair some machinery.
Meanwhile, earlier this year, she joined the Irish Guards on Salisbury Plain in freezing conditions to carry out battlefield drills.
