Prince Harry has recalled the time he received a "cold-blooded" Christmas present from Princess Margaret when he was a teenager.
The Duke of Sussex opened up about family feuds as well as his relationships with several royals in his memoir Spare, which was published earlier this month.
One of the family members he mentions in his book is Princess Margaret, the late Queen's sister.
Harry refers to his great-aunt Margaret as "Aunt Margo" and claims he didn't know her very well despite sharing "12.5 per cent" of her DNA.
In his memoir, the Duke says that they usually spent family holidays together but Princess Margaret was "almost a total stranger" to him.
Harry says that on a Christmas Eve at Sandringham Estate when everyone was getting ready to open their gifts, his great-aunt Margaret gifted him an unusual present - a tiny biro with a rubber fish wrapped around it.
He wrote: "Standing before my pile, I chose to open the smallest present first. The tag said: 'From Aunt Margo'. I looked over, called out: 'Thank you, Aunt Margo!'"
After opening the gift, Harry was surprised and thanked Margaret, who he claims pointed out that it was not just any biro, but a special one.
Harry added: "It wasn't just any biro, she pointed out. It had a tiny rubber fish wrapped around it.
"I said: 'Oh. A fish biro! OK.' I told myself: That is cold-blooded."
In his book, Harry adds that growing up he thought he and Margaret should have been friends as they were "Two Spares" and had a lot in common.
The memoir says: "Her relationship with Granny wasn't an exact analogue of mine with Willy, but pretty close. The simmering rivalry, the intense competition (driven largely by the older sibling), it all looked familiar.
"Aunt Margo also wasn't that dissimilar from Mummy. Both rebels, both labelled as sirens."
Princess Margaret died on February 9, 2002, at the age of 71 after suffering a stroke. Harry said that after learning she had been taken ill, he thought he would have wanted more time to get to know her properly.
However, as he explains in his book, they were "well past that" as at that point, Margaret was "unable to care for herself" and her health was "swiftly declining".
Margaret was last seen in public in both August and December 2001, the first when she appeared at her mother Queen Elizabeth The Queen Mother's 101st birthday celebrations and then for her aunt Princess Alice, Duchess of Gloucester's 100th birthday celebrations.
Her funeral was held on the 50th anniversary of her father's funeral on February 15 - a week after her death.
There were around 400 mourners at the funeral - including an unwell Queen Mother who died two months later.
Margaret's ex-husband Lord Snowdon was in attendance, along with her close friend and former lover Roddy Llewellyn.
The Princess' grieving children Viscount Linley and Lady Sarah Chatto and their partners attended the ceremony too, along with The Queen and her family.
According to reports, Prince Harry made £16million from Spare after earning £109million in Spotify and Netflix deals.
In the UK, 750,000 copies of his memoir have been sold since it was published earlier this month.
JJ Moehringer, the book's ghostwriter, was paid $1million (£810,000) for writing the book.
Harry has so far given £1.2million of the proceeds from Spare to charity.
