Heath Ledger fell in love with Michelle Williams ''at first sight.''

'Brokeback Mountain' screenwriter Diana Ossana says the late Australian actor, who died from an accidental drug overdose in January 2008 just months after he and the actress ended their three-year relationship, formed an immediate bond with her on the set of the film in 2005.

Reflecting on the former couple's real life love story in honour of the movie's upcoming 10th anniversary, she told OUT magazine: ''The first day we filmed that scene where Michelle's character is on the toboggan and falls off the sled, and Ennis [Heath's character] is with her -- they're laughing; well on the third take, Michelle fell off the sled, and at the bottom of the hill she was crying.

''She'd twisted her knee, and we had to call someone to take her to the hospital. Heath was not about to let her go alone, and as he was getting into the vehicle with her he was smoothing her hair back. I remember him looking at her, and she looking up at him with these wide eyes. She was almost startled by the attention he was giving her, but you could see it every day from thereon. For him it was truly love at first sight. He was so taken with her.''

Former 'Dawson's Creek' star Michelle, 34, gave birth to their daughter Matilda, now nine, shortly after they completed shooting the film.

The actress previously admitted she and Heath had a ''cosmic'' connection from the first time they met.