They're the royal brothers who have become the best of friends.
From a young age, the princes were inseparable. Prince Harry was just 12 years old when his mother Diana, Princess of Wales, died, while William was 15. The tragedy deeply affected both boys, but they always had each other.
But as Prince William, 36, and Prince Harry, 34, forge their own paths with their respective wives, families and royal careers, the pair will soon go their own ways in a symbolic parting of the royal households.
A new report by royal correspondent Roya Nikkhah for the Sunday Times reveals William and Harry will create two separate courts as their roles with Kate and Meghan evolve.
What's more, as Harry and Meghan countdown to welcome their first child next year, they're also looking to move out of Nottingham Cottage, which is right next to William and Kate's 1A residence at Kensington Palace.
"The Sussexes are expected to leave their two-bedroom home at Nottingham Cottage, in the grounds of Kensington Palace, and may choose to move into the main palace or find a new royal residence," a well-placed source tells Nikkhah.
"The brothers have leant on each other and looked after each other since their mother died. But now they have their own families, they no longer rely on each other as before."
The insider adds: "[The] William and Harry double-act has naturally been supplanted by the two couples and their families. They have become different people with different outlooks on life. Splitting the household is the obvious thing to do."
As the "fab four", as they've been affectionately dubbed, branch off into separate courts as husband and wife we can expect to see the Duke and Duchess of Cambridge continue their more formal duties as King and Queen consort-in-training.
WATCH: Duchess Meghan delivers a stirring speech in New Zealand. Post continues...
Meanwhile, the Duke and Duchess of Sussex have more flexibility as they are further down the line of succession but will continue to champion issues impacting the youth of the Commonwealth, including mental health, veterans, and gender equality - as demonstrated on their most recent royal tour of Australia, Fiji, Tonga and New Zealand.
But it's not the end of an era just yet! We'll still see William, Kate, Harry and Meghan come together through their joint organisation The Royal Foundation, and of course at official family events.
And while William and Harry may not be as reliant on one another as they once were, there's no doubt the siblings share an unbreakable bond.