By Stephen M. Silverman
Updated March 16, 2004 03:01 PM

Handsome British actor Terence Stamp — last seen baring his butt to Ashton Kutcher in the sub-par comedy “My Boss’s Daughter” — had an affair with Princess Diana, according to a new book by noted Diana biographer Andrew Morton that’s scheduled to be published this summer.

According to British press accounts, Stamp, now 64, was one of three public figures who had affairs with Diana, claims Morton in his upcoming “Diana in Search of Love.” (Morton’s definitive 1992 “Diana Her True Story,” which had the cooperation of the princess, was an runaway international bestseller.)

Her affairs were with “a married film star and a captain of industry who is a household name”, Morton claims in his book, according to Britain’s Daily Mail.

Stamp reportedly met Diana at the 1987 London premiere of the movie “Wall Street,” in which Stamp had a role. At the time, Diana’s marriage to Prince Charles was reported to be crumbling.

In a recent interview quoted by the Mail, Stamp admitted flirting with the princess.

“She started all the official stuff, and I just said, ‘Oh stop that,’ and told her I’d seen her dancing that time in Covent Garden and how good she was,” Stamp reportedly admitted. “She truly blushed.”

Stamp, whose former lovers include Joan Collins and Julie Christie, reputedly invited Diana to lunch at his apartment — the meal consisted of brown-rice and mushroom risotto, apparently for starters — and helped coach her in public speaking.

She, in turn, reportedly barraged him with letters of admiration.