Princess Diana's Shocking Words After Her 1985 'Uptown Girl' Dance Revealed (Exclusive)

The late Princess of Wales' former ballet teacher remembers what she said when the curtains closed

Princess Diana had a surprising reply to the roaring applause after her unexpected "Uptown Girl" performance for the future King Charles nearly 40 years ago.

In the new book Dancing With Diana: A Memoir, out Sept. 10 and exclusively excerpted in this week's issue of PEOPLE, dancer and ballet mistress Anne Allan reflects on what it was like to give the late Princess of Wales hundreds of secret one-hour ballet lessons from 1981 to 1989. Allan revisits how their discreet sessions sparked a close bond and gave the princess an outlet for her most intimate struggles—including her battle with bulimia and the increasing unhappiness in her marriage to Charles.

One passage of the revealing new memoir looks back at how Diana decided to surprise her husband by dancing to Billy Joel’s "Uptown Girl" on stage at a charity event at the Royal Opera House in London in December 1985. Princess Diana performed the choreography with her friend Wayne Sleep, the acclaimed British dancer, as a special surprise for Prince Charles—who was allegedly less than impressed with the three-minute routine.

The surprise that backfired was later immortalized in season four of The Crown on Netflix, and Allan witnessed the future King's frosty reaction first hand.

"She just wanted him to be thrilled," Allan tells PEOPLE, believing that Diana was eager to impress Charles. "When you feel that somebody doesn’t love you, that has an effect on you. She kept thinking that there was love there and that there would be love there. And I’m sure there was."

Allan has rarely spoken about her time with Diana, and shares what she said after the curtains closed at the Royal Opera House in the exclusive excerpt below.

Related: Tom Selleck Reveals Why He Almost Declined a Dance with Princess Diana at 1985 White House Dinner

When she entered, there was an audible intake of breath from the audience. Diana quickly and confidently completed her first steps of a jazz strut across the stage, and a thunderous applause erupted. The audience could not believe what they were seeing. She had been choreographed to stop for two bars of music, look at the audience, give a couple of jazz shoulder rolls when she saw the Downtown Boy, then continue with some jazz slides to see if he was following. Next was her favourite moment, placing her hands on Wayne’s head and pushing him down into a kneeling position, then kicking one of her legs high over his head. The audience loved the storytelling of the move.

The dancing couple went back out for their curtain calls and had to take several, till Wayne decided that was enough. "Let’s leave them wanting more," he said. As she came off from the final bow, Diana said to both of us, "Beats the wedding!" Wayne and I were astounded.

. . . As we were led to the reception area where Charles would be, we passed many members of the audience who congratulated her, which she truly loved. . . . She made her way to Charles, and as she stood before him, I could sense she desperately wanted his approval. He said, "Well done, darling," and turned to talk with someone else. I sensed disapproval from him and my heart took a thud. 

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Read the original article on People.