They were the closest of brothers, with the loss of their mother only solidifying the fraternal bond between Prince William and Prince Harry as they grew up.
But, now, as married men with responsibilities, cracks appear to be showing in their relationship – and it could be their wives who are pulling them apart.
It emerged yesterday that Harry and his wife Meghan are to move out of Kensington Palace next month to set up home at Frogmore Cottage on the Windsor estate.
READ MORE: • Harry and Meghan leave Kensington Palace
News of the move comes after reports that the princes, who both have homes at the Palace, may be ready to set up separate courts.
The developments could reignite speculation of a rift between the Royal siblings – but a close friend of the Cambridges last night suggested any unease was between their wives.
"Kate and Meghan are very different people," the source said, adding: "They don't really get on."
Harry and mother-to-be Meghan have been given Frogmore Cottage by the Queen, and it will become their official residence.
On the face of it, there are good logistical reasons for the move.
Frogmore has ten bedrooms compared to just two at Nottingham Cottage, the Kensington Palace property where they currently reside.
It would also allow Meghan's mother Doria, who has just moved to the UK, to join them, and there would be room for a live-in nanny.
Grade II listed Frogmore is said to be undergoing a multi-million pound refit, paid for by the taxpayer, in preparation for the birth, which is expected next spring.
Palace sources said there was "nothing available as an official residence in London". One said: "They are expecting a baby early next year and obviously need a bit more space. It is not like this has just come up."
The couple chose Windsor because "it means a huge amount to them – it is where they got married."
Rumours of tensions between the Sussexes and Cambridges have been bubbling away for months.
In contrast to Meghan and Harry's cottage at Kensington Palace, Kate and William have a 22-room home recently refurbished at a cost of £4.5 million.
The Sussexes wanted to move into a Palace apartment currently used by the Duke and Duchess of Gloucester.
But sources claimed the apartment "needs to undergo considerable lengthy refurbishments' meaning that no one else could move in "for the foreseeable future".
In fact, they said, the Gloucesters were happy to downsize into a smaller property.
The pair will move to the Old Stables in a different part of the palace grounds in the new year.
Meghan has shaken up the Royal Family and earned a reputation among courtiers for a direct approach.
Earlier this month, there were even claims that the Queen had felt compelled to speak to Prince Harry about Meghan's attitude in the run-up to their wedding, following a disagreement over which tiara she would wear.
Earlier this year, it emerged that Harry and William were considering a formal division of their joint household at Kensington Palace.
It was reported that separate courts would "better reflect their very different duties and needs" following Harry's marriage to Meghan.
READ MORE: • Queen's pre-wedding row with Meghan
In the past, Harry has said he expects the world's interest in him to fade as the Cambridges' children grow older. William, meanwhile, is set to see his workload increase as he prepares to one day become King.
Kensington Palace declined to comment last night.