The Queen and Prince Philip with Princess Anne and Prince Charles in 1951. Photo / Getty Images
"It's a matter of convenience, if you can afford it," he said, referring to his and his wife Mira's separate bedrooms.
"If you can have that extra room, it's basically a luxury."
Reports have also emerged that Prince Philip was "leading a separate life" to Her Majesty.
The Daily Mail reported the 98-year-old spent most of his time in Windsor or Wood Farm — a modest cottage on the Sandringham estate.
A courtier told the publication: "The Queen feels the Duke has earned a proper retirement. She knows him too well — if he was still at the centre of royal life he'd feel he had to be involved.
"Being at Wood Farm means that he's not too far away but far enough to be able to relax."
The Queen is currently enjoying some time away from the spotlight at her home in the Scottish highlands.