Before he stepped out of the shadows as "The Batman" or played a non-bat vampire who sparkled in sunlight in the "Twilight" movie series, Robert Pattinson was just an up-and-coming young actor trying to prove himself on the set of "Harry Potter and the Goblet of Fire." The fourth Potter film saw Pattinson take on the role of Cedric Diggory, a Hogwarts student who competes with Harry Potter himself (Daniel Radcliffe) in the Triwizard Tournament.

The tournament involves three tasks, which Hermione Granger (Emma Watson) says "are designed to test you in the most brutal way." You might think a movie about a Goblet of Fire would steer clear of the water, but the second task sent the Triwizard champions plunging into the Black Lake.

For Pattinson, it turned into a literal sink-or-swim acting challenge. In a press junket to promote the theatrical release of "Harry Potter and the Goblet of Fire" back in 2005, the actor confessed (via Diagon Alley):

"Even though my press release says I'm really good at swimming and sports and stuff, I'm actually not. So I had to kind of get better at swimming very quickly. And yeah, just sort of holding your breath for 30 seconds or whatever seems like it's relatively easy, like if you're just kind of swimming around on holiday or whatever, but having to do it on cue and just when they say 'action' and you have to just swim from there to there, but you can't see anything. That's the annoying thing. And also you've got to be acting."

Harry Potter And The Diving Certificate

Robert Pattinson wasn't the only one tested by the underwater scenes in "Harry Potter and the Goblet of Fire." In the DVD featurette, "In Too Deep: The Second Task," producer David Heyman revealed that, for the whole cast and crew, "the biggest challenge in terms of filmmaking was the underwater task." They opted to shoot underwater for real because the filmmakers felt close-ups couldn't be done as well if they tried to recreate them another way.

According to the Warner Bros. Studio Tour London – The Making of Harry Potter, the production employed Europe's largest underwater filming tank and Daniel Radcliffe spent so much time swimming around in it that he got his diving certificate. In the aforementioned press junket, Pattinson also related how the low visibility underwater meant he would sometimes be swimming toward the wrong shape, thinking it was a diver with a breathing apparatus for him, only to be left with his "stupid face just like screaming underwater."

Pattinson has since gone on to bigger and better things than his one-off supporting role in "Harry Potter and the Goblet of Fire," so it's safe to say he lived up to the challenge of filming those underwater scenes. And who knows, his experience there might have even come in handy later, increasing his lung capacity to a superhero level for when he had to shoot scenes in a flooded Gotham City in "The Batman."

With "The Batman: Part II" on the way in 2025, Pattinson will soon be headlining his own big-budget sequel from Warner Bros, while the "Harry Potter" franchise will face its own uphill battle of rebooting the beloved eight-movie series as a new HBO show no one asked for, all while overcoming the controversy surrounding creator J.K. Rowling's involvement.

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