They were once the ultimate brothers and best friends.
But in recent months, the divide between Prince William, 36, and Prince Harry, 34, has been easy to see.
From that frosty appearance over Easter, to the fact Prince William will be in New Zealand while Harry's first-born is believed to be due, the extreme change in dynamic between the once jovial pair is concerning.
And now, further details on their rumoured rift have come to light after royal reporter Katie Nicholl, who has written a whole book on the topic called Harry and Meghan: Life, Loss and Love, appeared on Fox News.
According to the respected royal commentator, things went "badly" after William tried to warn Harry over how fast his romance with the American actress was progressing.
"William was concerned about how quickly the relationship had moved and wanted to make sure that Harry was making the right decision," Nicholl explained.
"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."
WATCH: Prince Harry and Prince William watch old family movies together. Post continues after the video...
"William is very protective of Harry. He loves Harry - but their relationship was always going to change when Harry married," she added.
"And very reliable sources have told me that the relationship has gone through really challenging times since Harry and Meghan started dating."
However she believes the Sussex's recent move to Frogmore Cottage in Windsor and away from the fishbowl of Kensington Palace, where Prince William and Duchess Catherine live, will be hugely beneficial for the relationship.
"Moving forward, with the benefit of not living on top of each other, I think their relationship will go from strength to strength from now on."
"I hope so, because they're not just two of the world's most popular princes, they're two of the world's favourite brothers."
Despite his initial concerns about Meghan, Nicholl believes William is warming to her.
"I think William has realised that Meghan is probably the best thing to happen to Harry. I think he's impressed too by her work ethic."