The princess’s dance partner spoke out about their big number, which was included in The Crown Season 4.

Season 4 of The Crown introduces a handful of “Did that really happen?” moments, from Prince Charles’s cringeworthy engagement interview to the queen’s secret estranged cousins. Also among those in the list is Princess Diana’s surprise dance number at the Royal Opera House—this, much like most of the events in the show, did happen in real life.

In December 1985, Charles and Diana attended a gala performance at the storied venue. Midway through, the princess quietly left her seat in the Royal Box to grace the stage with dancer Wayne Sleep. They danced to Billy Joel’s “Uptown Girl,” which was Diana’s own song choice.

“There was a gasp from the audience, of 2,500 people, who took an intake of breath all at the same time. They were speechless,” Sleep recalled in a video about the performance years later.

Can you watch the performance online?

Unfortunately, there is no video of Diana’s big dance number. (It was the ’80s; people weren’t going to whip out their phones to record.) And there were only a few black-and-white photos of the set taken by the opera house’s photographer, which were published in 1995, according to Town & Country.

The next best thing to an actual recording is this video of Sleep in 2017, 20 years after Diana’s death, in which he retraces the steps from the dance for CBS’s 48 Hours.

How did it all come together?

Sleep had known the princess since the early 1980s, when she approached him for dance lessons, he revealed to The Guardian. He couldn’t teach her because he was always on tour as a professional dancer, but she later came to him again to propose their big gig. “It was all top secret,” Sleep explained.

He and the princess rehearsed privately in a studio in West London. “She was in leg-warmers and a leotard,” he added. “My first thought was, she’s too tall to dance with me, I’ll be a laughing stock: I’m 5ft 2in and she’s 5ft 11in. But I soon realised she had a good sense of humour, and that we could have some fun with our height difference. She’d already decided on the music: Billy Joel’s Uptown Girl.”

As for Diana’s song choice, Sleep explained to Vulture, “There was a music video that went with the song and she must’ve seen the video. There’s a lovely lady with a hat—she’s very chic and gets out of a car. Diana knew she could play that role of sophistication.”

The night of, Sleep signaled to Diana from the wings of the stage that it was time for her to get backstage. The piece opened with Sleep but Diana made her grand entrance soon after, leaving the audience in shock. The choreography had turns, high kicks, and even a lift of sorts. Diana wasn’t playing around.

How did Prince Charles react?

In The Crown, Josh O’Connor’s Charles is upset by this surprise, as he thinks Diana is trying to show off and upstage him. (The gala was hosted for his 37th birthday, after all.) The stunt exacerbates his already-present irritation over how well liked and popular his wife is.

In real life, it’s unclear exactly how the prince felt, though some accounts suggest that he was unhappy with the performance. Per Vanity Fair, one of Diana’s biographers, Tina Brown, wrote that Charles was cool and detached after the performance. “It was embarrassingly clear that he had not been ravished by the spectacle of his wife en pointe. His disappointing response, when it leaked, was interpreted as frigid disapproval of Diana’s lapse in royal etiquette.”

But Sleep said that things were fine, at least from his point of view at the after-party. “He had a raised eyebrow, you might say. It didn’t go any further than that at the party,” he told Vulture.