The stars who secretly hooked up during filming of 10 Things I Hate About You

Heath Ledger and Julia Stiles' relationship in 10 Things I Hate About You spilled into real life too. Photo / Supplied

10 Things I Hate About You was the teen movie that made an entire generation fall in love with Heath Ledger - including one of his co-stars.

In what's sure to add an extra layer of bittersweet nostalgia to your next viewing of the 1999 hit film, it's emerged the romance between Julia Stiles' character Kat Stratford and her on-screen love interest Patrick Verona (played by the late Heath Ledger) reportedly spilled over into real life.

According to commentary by other cast members in a special edition release of the DVD, the two stars felt sparks on the set and fell in love while filming, but broke up in early 2000.

Heath Ledger and Julia Stiles in 10 Things I Hate About You. Photo / Getty Images

Despite never publicly confirming it, Stiles certainly has nothing but positive things to say about her "amazing" times alongside Ledger.

"He was so nice. He was such a force; he was - even at that age - a very, very powerful, lovely human being," she gushed in an interview with US Magazine in 2014.

It's a sentiment echoed by David Krumholtz, who played geeky Michael Eckman. In late 2015, he opened up to NY Mag with new details of his time with the late Australian star.

Ledger was the last lead to join the cast, arriving on set a week into filming because of his commitments on the Aussie TV series, Roar - and Krumholtz confessed the rest of the cast was initially concerned about how he'd fit in.

"We had only heard stories from the producers about the disarming charisma of a handsome Aussie from Perth with an infectious smile," he remembered.

"We had all established such strong friendships...We worried about how someone named Heath could possibly manage to find his place in our inner circle."

But that hesitation quickly vanished when Ledger arrived. "The group, with Heath, only got stronger."

Reliving the memories of the cast's instant bond, he revealed: "Work was fun, and after work we were inseparable. We laughed, we partied, we rapped. But it was Heath - a natural storyteller, and always reliable for a cheesy joke - who transfixed us."

Testifying to Ledger's mark on many, he concluded by expressing gratitude for the opportunity to work with the late actor.

"I was lucky to be there, I was lucky to be with that cast, and I was extremely lucky to have made friends with a normal, everyday guy named Heath, whose enthusiasm and talent were boundless, who shined in every single frame of film."

"Who can ever forget Heath Ledger singing You're Just Too Good to Be True with the backing of a high-school marching band in the film's glorious climax? I certainly can't."