JASON ISAACS was stunned to hear about the death of his THE PATRIOT co-star HEATH LEDGER - and immediately rang the movie’s other stars to mourn the tragedy.

The pair starred in the 2000 war movie, alongside Mel Gibson and Joely Richardson, and kept in contact after filming had wrapped, meeting up whenever their schedules allowed.

Ledger’s untimely death from a prescription drug overdose in January 2008 devastated Isaacs, who felt compelled to reminisce about the actor with his former co-stars.

He tells Total Film magazine, “All of us who’d worked with him on The Patriot, when we heard the news, people who hadn’t spoken for years were phoning each other - we just wanted to somehow connect. He was a very sweet boy.”

Isaacs remembers his last meeting with Ledger with great fondness - because the late star had just discovered he had landed the role of The Joker in Batman movie The Dark Knight.

Isaacs adds, “The last time I saw Heath was at Soho House. He said, ‘I’m about to play The Joker.’ I went, ‘F**k, are you? Nightmare!’ He said, ‘I know, I know.’ I said, ‘Did you watch the other one?’ He said, ‘No! Don’t be mad, that’s not gonna help is it? I’ve got this notepad and I’m just writing down ideas.’”

Ledger posthumously won this year’s (09) Oscar and Golden Globe awards for Best Supporting Actor for his portrayal of The Joker.