Paul Burrell has claimed Prince Harry will be feeling "painful emotions" when he returns to the US after Prince Philip's funeral.
The British royal moved to the United States last year with his wife Meghan, Duchess of Sussex, and he flew home last week to attend his grandfather's memorial following his passing at the age of 99.
Paul - who was butler to Harry's late mother Princess Diana and helped raise the young prince and his older brother Prince William - explained how seeing his family again after the couple's recent tell-all interview with Oprah Winfrey will have been particularly difficult.
He told Closer magazine: "Harry's world was torn apart when he left the UK and moved to California last year - and now he's faced with the consequences.
"And in such devastating circumstances - to commemorate the loss of his grandpa. Being back in the UK, seeing his family - the family he has criticised - is extremely difficult."
Paul pointed to Harry being back in such familiar territory as a definitive reminder to him of the "decision he's made" to step back as a senior member of the Royal Family and start a new life in America with his pregnant wife - formerly known as Meghan Markle - and their 23-month-old son Archie.
He added: "Seeing his beloved granny, the Queen, and to face his father and brother would not be easy. Even submerging himself back into the House of Windsor and the buildings that hold so many memories.
"The chapel - the same chapel where he married Meghan almost three years ago - in very different circumstances.
"It will have stirred up all kinds of painful emotions for him. He will really have felt the impact of the decision he's made now and it'll hit home."
Paul's comments come after Harry reportedly met with Prince Charles, Prince William and Duchess Catherine for "clear-the-air talks".
The 36-year-old royal is believed to have met with his father, his brother, and his sister-in-law to begin mending the rumoured rift between them which surfaced after the tell-all interview last month.
Harry is thought to have hosted his family members at his former home in Frogmore Cottage - where he lived with Meghan until they moved to California last year - after he temporarily returned to the UK last week ahead of Prince Philip's funeral over the weekend.
A source said: "Harry obviously felt outnumbered as there are three of them and only one of him so wanted it to be on his home turf.
"There is no way this is the end of the crisis in their relationships but it's a good gesture and a nice way to take the first step towards healing."