Watch the moving trailer for new Heath Ledger doc

I Am Heath Ledger features home movie footage shot by The Dark Knight star, as well as interviews with Naomi Watts, Ben Mendelsohn and Ang Lee

A new documentary on much-missed actor Heath Ledger – who died age 28 from an accidental prescription drug overdose in 2008 – will premiere at Tribeca Film Festival on April 23, and its trailer, released online last night, suggests it’ll be an emotional watch.

Ledger is best known for his knockout turn as The Joker in The Dark Knight, for which he won a posthumous best supporting actor Oscar, and heartbreaking drama Brokeback Mountain, which told a love story of two young men – Ledger’s ranch-hand and Jake Gyllenhaal’s rodeo cowboy – in 60s America.

As well as revisiting these famous roles, the documentary looks to include interviews with a host of Ledger’s family, friends and colleagues.

In the trailer, we hear fellow Australian actor Ben Mendelsohn discuss his admiration for Ledger’s daring as an actor. "Before Brokeback Mountain came out it would have been unthinkable to have a romantic tragedy involving two gay cowboys,” says Mendelsohn in the doc. “This is one of the biggest heartthrobs on Earth taking on that character – that's an artist."

Ang Lee, Ledger’s director on Brokeback Mountain, says that "even as a supporting actor he will steal the whole show. That's the power of Heath Ledger."

The film, called simply I Am Heath Ledger, also reveals the actor’s desire since an early age to be a director. "There were always cameras around, a video camera, a Polaroid camera or the film camera," says model Christina Cauchi, who once dated the actor. "That's the only way I think of him." Directed by Derik Murray, much of the footage from the documentary seems to use this huge archive of home video material filmed by Ledger himself.