Hairspray Director Recalls Watching John Travolta, Christopher Walken Waltz: 'What Am I Looking At?'

Courtesy Warner Bros. Christopher Walken and John Travolta in Hairspray (2007)

Adam Shankman won't forget John Travolta and Christopher Walken's onscreen connection anytime soon.

In an interview with PEOPLE about Hairspray's 15th anniversary on Wednesday, the iconic movie musical's director says he will "never forget the first time that I got John Travolta and Chris Walken in to rehearse" their duet "(You're) Timeless to Me," complete with a dance.

"I was sitting there in the rehearsal stage and the two of them were waltzing ... and I was going, 'Oh, my God, what am I looking at?' " says Shankman, 57. "'Cause it was John Travolta and Chris Walken doing a love song."

"It was all very surreal," he recalls.

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Courtesy Warner Bros. John Travolta and Nikki Blonsky in Hairspray (2007)

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Travolta, now 68, and Walken, now 79, played parents to Nikki Blonsky's Tracy — Edna and Wilbur Turnblad, respectively — in the 2007 film.

Recalling her own experience seeing "pro" Travolta dance for the film under his bulky costume, Blonsky, 33, tells PEOPLE he was "so incredibly light on his feet" and made it "look effortless."

She also calls the Grease icon "an incredible actor to work with," even aside from his talent.

"He was so nice to every single cast member, every extra, every person on set," Blonsky says. "That is what set the tone for basically the amazing experience we all had because everybody was just so excited every day to show up, to work, put on our costume and work with John."

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Both Walken and Travolta have several musical projects under their belts aside from Hairspray. The latter has starred in films like Grease (1978) and Saturday Night Fever (1977). Walken, meanwhile, appeared as Captain Hook in 2014's Peter Pan Live!, and dances through a hotel in Fatboy Slim's 2001 music video for their song "Weapon of Choice."

And while Shankman tells PEOPLE that the Hairspray cast is "super busy" nowadays and, as a result, aren't able to see each other in person too often, they "give each other virtual love."

Asked if he'd be down for an in-person reunion, the filmmaker adds, "If they get a screening at the Hollywood Bowl or at the [Hollywood Forever] Cemetery or something like that, I would try to get out as many people there as I could, but people are all over the place working. Everybody's booked and blessed. I'm super happy for everybody."