American filmmaker Mike Mills always knew that there was something different about his parents' marriage.

His suspicions were confirmed in 1999, after his mother's death from cancer.

After 45 years of marriage, Mills' father, Paul, made a life-altering announcement to his son and two daughters.

The family's 75-year-old patriarch was gay.

"One minute I was worrying about how my widowed father was going to defrost food on his own in the microwave. The next minute dad was gay," Mills, 45, told recently during a sit-down in Toronto.

"My parents both knew dad was gay when they married. They loved each other in their own way," Mills said.

"But the minute dad came out he became so alive. He wanted to do new things and talk about everything. I was hungry to talk to him and listen."

That transition and the legacy of emotional confusion left by his parents' deaths in 1999 and 2004 became the inspiration for Mills' latest movie, "Beginners."

Pieced together by fact and fiction, Mills has created a powerful, heartfelt portrait of his father that is made all the more absorbing by the film's stars.

Christopher Plummer, 81, plays Hal, a witty, engaging figure who leaps out of the closet in his seventies and into a vibrant new life as a gay man.

Hal joins gay book clubs. He throws exuberant parties for his new gay friends. Hal even lands himself a much younger lover.

Out of the closet at last, Hal revels in every moment. That joy is bittersweet, however. Hal is secretly dying from lung cancer.

Ewan McGregor, 40, portrays son Oliver, a commitment-phobic graphic designer who is jealous of his father's emotional bravery.

"I would never have had the nerve to think of some as handsome as Ewan playing me," Mills said, with a grin.

"But Ewan and Chris matched each other visually. You look at them and you think, 'Yeah, these guys really could be father and son.'"

Mills helped that connection along by sending his stars on a shopping expedition at Barneys before "Beginners" began shooting.

Mills gave McGregor $200 and asked him to buy Plummer a scarf. The actors ended up buying several pairs of skinny jeans along the way, as well as the scarf Mills requested.

"Christopher and Ewan are pros," said Mills.

"They made all those feelings that I had about my father and my childhood present and communicable in their performances. But this was no imitation of my father and me," he said.

"These guys owned their roles. My father would have loved that if he were alive today."

'Beginners' dad an inspiration

Mills' route to Hollywood was never planned.

The one-time graphic designer stumbled into filmmaking after seeing Errol Morris' 1988 documentary, "The Thin Blue Line."

"Something inside me just clicked when I watched it," said Mills.

"I knew in that instant what I'd always been trying to do with my life."

Mills went on to create music videos for artists like Moby and Yoko Ono. He shot commercials for the Gap, Adidas, Nike and other blue-chip brands over the years.

His Hollywood breakthrough came in 2005, when Mills' quirky film, "Thumbsucker," became a huge hit at the Sundance Film Festival.

The movie's release came just before Mills' father passed away in 2004.

During his lifetime, Mills' "bossy," art historian dad had been the director of the Santa Barbara Museum of Art.

"He'd come to my sets and look around and say, 'That's not right' or 'This feels all wrong," said Mills.

"But both my parents understood art. They'd totally get that this movie isn't about destructive accusations or lingering ghosts. It's just my version of our life together," he said.

"First and foremost, 'Beginners' is a story about having the guts to reclaim your life. It's my psychic inheritance from my parents. This is how I spent it."