Rumours of the royal rift have been swirling for so long now, it's hard to know who is meant to have said what to whom, and when.
However, royal biographer Katie Nicholl has shed some light on where the beef between the Cambridges and the Sussexes may have stemmed from.
The author has recently published a book which examines Prince Harry and Meghan Markle's relationship in detail.
This in-depth look at their romance also involves analysis of Harry and Prince William's relationship, which Nicholl claims started running into rough waters around the time Harry and Meghan started dating.
'You've been Meghan Markled' appears on Urban Dictionary - and it's not flattering
According to the author, William expressed some concerns over their budding romance, and Harry took it badly.
Speaking to Fox News, she said: "William was concerned about how quickly the relationship had moved and wanted to make sure that Harry was making the right decision.
"What was intended as well-meaning, brotherly concern and a bit of advice went down quite badly with Harry, who felt William wasn't being as supportive as he might have been."
Meghan Markle and Harry share sweet photos and birthday message to 'granny' the Queen
She continued: "William is very protective of Harry. He loves Harry - but their relationship was always going to change when Harry married.
"And very reliable sources have told me that the relationship has gone through really challenging times since Harry and Meghan started dating."
The Sussex's move to Frogmore Cottage , Katie feels, will be beneficial to the brothers' relationship.
Telltale difference between capturing Meghan Markle and Kate Middleton on camera
Katie also notes that as time has gone on, William may very well have warmed to Meghan because of her positive influence on his brother.
"I think William has realised that Meghan is probably the best thing to happen to Harry," Katie added. "I think he's impressed too by her work ethic."
