King Charles is marking his 76th birthday with a day of charity engagements on Nov. 14, but back in 1985 he celebrated in a much different way—at least according to Netflix’s The Crown.

In a season 4 episode titled “Avalanche,” Princess Diana takes the stage to surprise her husband with a special birthday dance. While the performance actually did happen in real life, it played out in a much different way, according to her dance instructor’s book, Dancing With Diana.

In her memoir, Anne Allan—who started giving Diana private dance lessons in 1981—wrote that ahead of Christmas 1985, the royal had expressed “how lovely it would be to feel what it was like to do a performance.”

The plan was not to do the dance as a 37th birthday gift for Prince Charles, as The Crown depicted in season 4 (the real performance took place on Dec. 22, per Allan). In reality, it was a “dream” of Diana’s to perform in public, but the princess’s idea wasn’t entirely well-received at first.

Per Allan, Princess Diana had the idea to hit the stage during the Annual Friends Gala at the Royal Opera House in London—taking the dance teacher completely off guard. “I gulped!” she wrote, adding, “That was a whole other world. I didn’t even know how to react.”

The dancer continued that she “wasn’t at all sure that it was a good idea,” but Princess Diana had her mind made up, down to the song choice of “Uptown Girl” by Billy Joel (hilariously pronounced as “Billy Joe-elle” by Queen Elizabeth in The Crown).

Allan wrote that she was concerned about “rumblings in the press” regarding the prince and princess’s marriage and how Diana had told her that “Charles much preferred opera to dance.” He also, per the princess, didn’t share the same taste in music.

However, Diana remained undeterred, and Allan wrote, “I decided to see if I could make this dream of hers happen.” Sleep ultimately agreed to do the routine and the dancer, who was just 5’2, created the choreography to use their eight-inch height difference “to their advantage in a humorous way.”

The dance instructor also pointed out “that the rehearsals we had did not take place at Kensington Palace, as indicated on Netflix’s The Crown, but in the dance studio where we had been working out since 1981.”

On the night of December 22, 1985, Princess Diana joined her husband in the royal box to take in a variety of performances, but at one point, she slipped off. In the Netflix drama, Charles stands up and applauds uproariously for an opera number before taking his seat and watching Wayne Sleep take the stage.

Allan wrote that in real life, a “very hyper” Diana had disappeared to The King’s Smoking Room, where she “was pacing and eating at a voracious rate from the table, which was covered in goodies.” The princess then joined Sleep as “Uptown Girl” started to play, and just like in the Netflix show, the crowd went wild when they realized it was the Princess of Wales.

In the Netflix version of the performance, Charles stays in his seat clapping awkwardly while the rest of the crowd jumps to their feet. And while Charles and Diana are riding home from the event, he tells her it was a "grotesque, mortifying display." While we’ll probably never know what he really said, Allan penned that the future King’s reaction in real life was similar.

Allan wrote she could “sense” that Diana “desperately wanted his approval” during a reception after her dance performance. However, Charles simply said, “‘Well done darling,’ and turned to talk with someone else,” Allan wrote.

In January, when they returned to lessons for the first time after the holidays, the dance instructor penned that Diana flashed “a naughty grin” and “admitted that she didn’t think Charles thought it appropriate" for her to dance in public.

However, Allan revealed that Diana had a three-word reaction after completing the dance, exclaiming backstage, “Beats the wedding!”