Princess Anne once made a joke about her brother Prince Charles one day becoming king by buying him a toilet seat, unearthed accounts show.
The Royal Family's Christmases are known for being quite the gathering and the Queen has always reportedly encouraged the family to buy fun gifts for each other.
One year Princess Anne - who is known for her witty comebacks - delivered a gift to her eldest brother Charles that left the other royals in stitches.
"Gag gifts" amongst the family are a particular favourite, royal expert Katie Nicholl told Channel 4's 'A Very Royal Christmas: Sandringham Secrets' documentary.
She said: "If you can achieve something that is tongue in cheek and will have the Queen laughing, then you've really done well that Christmas. The more kitsch, the better.
"Nothing ostentatious, or terribly expensive or lavish, that doesn't really go down well with the Queen."
Ex-royal butler Paul Burrell claimed to witness some of the hilarious exchanges between family members.
He said the royals "love lavatorial humour".
One year, Anne gave Charles - who is next in line to the throne - a toilet seat.
Mr Burrell added: "It's the public school upbringing — and why wouldn't Prince Charles like a white, leather loo seat from his sister Anne?"
Former royal press secretary Dickie Arbiter also gave context on why this gift was appropriate for Charles.
He said: "What is it we used to call the loo? We would call it the throne. You go and sit on the throne.
"So buying a leather-bound loo seat was really Princess Anne's way of saying, 'Here you are, you've got your own personal throne'."
In 2018, the rumour started that Charles opts to carry his own toilet seat with him when he travels.
The rumour comes from royal biographer Tom Bower's 2018 piece ‘Rebel Prince: The Power, Passion and Defiance of Prince Charles’.
He described a list of items Prince Charles and Camilla have with them everywhere they go.
He added: "His staff had also made sure to pack a small radio, Charles’ own lavatory seat, rolls of Kleenex Premium Comfort lavatory paper, Laphroaig whiskey and bottled water for both bedrooms plus two landscapes of the Scottish Highlands.”
The claims have largely been put to bed with the Duke and Duchess of Cornwall both strongly denying it.
