Notes written by the late Princess Diana to British actor Terence Stamp have resurfaced at auction and are expected to fetch thousands under the hammer next week.

Stamp – who has featured in films such as The Adventures of Priscilla, Queen of the Desert and Superman II – passed away last August at the age of 87, and his personal collection of belongings are set to be auctioned by Bonhams on June 15.

However, it’s the notes written to him by the former Princess of Wales that have set tongues wagging, with the royal’s risqué sense of humour on full display in her written correspondence with the thespian.

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One letter, dated October 1991, saw the royal thank the actor for her “perfect” risotto lunch and open up about her personal struggles.

“Not many people would take the time and trouble to delve into such a complex situation… Three cheers for Prozac, not the American variety I hasten to add!” it read.

The antidepressant quip was followed by: “Lots of love Terence and a huge thank you, from Diana x”.

The intimate exchange is expected to fetch between £1,500 ($2,860) and £2,000 ($3,800) at auction.

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Other notes in the collection include Diana’s request to lunch with the actor via a postcard, which featured a bare female breast on the front, alongside the caption: “All the Breast from London”.

Another gag postcard sent to Stamp, which included a picture of a couple in bed, was captioned: “Why did God invent SEX?”.

The answer, which could be found inside the card, read: “So that married people do something at least twice a year”.

Diana then thanked her friend for the champagne at “lunch a la yeast” before signing off.

Stamp reflected on his friendship with Princess Diana in his 2017 memoir, revealing that he met the late royal through art dealer Oliver Hoare.

“She just wanted somebody to talk to that was a guy who would give her objective opinions,” he wrote.

“Because of that, we just kind of opened up to each other.”

“I saw the sadness in her because… she was a believer in the marriage and all that, and it didn’t turn out the way she expected it to,” he added, hinting at the failure of Diana’s marriage to now-King Charles III.

The auction will include several items from the late Golden Globe winner’s estate, including scripts, costumes, pictures, and furniture.

Ahead of the bidding, Bonhams’ head of popular culture Claire Tole-Moir dubbed the actor a “defining figure” of his time.

“Terence Stamp was not only an incredible actor whose long and varied career gave us many celebrated performances, he was also a defining figure of London in the swinging Sixties, emblematic of a certain style and charm,” she said.