Beginners is a deeply personal tale that marks Mike Mills’ sophomore effort following 2005’s Thumbsucker. Based on the writer-director’s own life, the film centers on Oliver (Ewan McGregor) as he comes to grips with the knowledge that his 75-year-old father (Christopher Plummer) is both gay and dying of cancer.

“It’s done with a lot of love and respect,” McGregor begins one afternoon in a suite at the Four Seasons in Beverly Hills.

Sporting an Errol Flynn-esque mustache and goatee – “It’s for the new Bryan Singer film, Jack the Giant Killer,” he explains – the actor describes hearing the story of Mills’ life and script.

“Rich Klubeck, who was Mike’s agent and is my agent now, he wasn’t at the time but he is now,” McGregor chuckles, “told me this lovely story as we were going up a chairlift, skiing in Sundance at the [film] festival. I had the script at home and read it as soon as I got back, then met Mike at this little café in Santa Monica and talked for hours. We didn’t discuss much about the script or the film, I just wanted to know more about his life, which shows [the story has] really landed in you; if you’re hungry for all those details. That was it, I was on board.”

The story cuts back and forth in time between the relationship Oliver has with his father and the first bloom of romance he finds with a beautiful but haunted French actress Anna (Mélanie Laurent, whom audiences will remember from Inglourious Basterds).

McGregor says, “We shot it as two movies. The first section was me and Christopher. We rehearsed for a week and then shot for two or three weeks, and then we stopped and rehearsed with Mélanie for a week and shot for two or three weeks.”

While it could be argued that Beginners is a duet of love stories – one between a child and parent, the other between two sweethearts – McGregor was more intrigued by the duality of each storyline.

“In the first story, it’s about a man who comes out in his 75th year, starts really living his life for the first time and blossoms, and, at the same time, he’s been diagnosed with terminal cancer and he’s dying,” he says. “In the second story, it’s two months after my father’s passed away, I’m in the depths of grief, experiencing all of that confusion and sadness, [and my character] is falling in love, which is the most wonderful experience in the world. It’s these two opposing things going on; I thought that’s a really great lot of stuff for an actor to play.”

Greatly aiding his performance was Mills, whom McGregor fawns over at every opportunity.

“Mike is so lovely,” the actor gushes. “He’s a brilliant, brilliant director. [Beginners is] Mike’s second feature film, and it looks like it was directed by a grand master. It was a real blessing for me as an actor to work with someone like Mike.”

The only being that draws greater praise is Cosmo, a Jack Russell Terrier who plays Oliver’s companion, Arthur, in the film. Asked if he had a hard time saying goodbye to his furry co-star, McGregor unabashedly admits, “It was impossible. And I haven’t really, I still see him now and again, and I’ve totally replaced him in my life with another little dog,” he laughs. “As I was nearing the end of the shooting, we [did] these interviews [on set]. It was the last week and I was talking about saying goodbye to Cosmo and I started to cry. I said, ‘Yeah, it’s been lovely to work with Mélanie and Christopher and next week,’” his voice cracks, and his face crumbles in mock-agony, “‘I have to say goodbye to Cosmo.’ I realized I didn’t want to be without Cosmo so I started looking for a dog to replace him, because he belongs to [the animal trainer], even though he felt like mine. I found my dog Sid at this rescue place called the Lange Foundation on Sepulveda on the last day of our shoot. He’s a beautiful dog, the exact same size as Cosmo, because it was too devastating to leave him.”

Beginners releases in select theaters June 3.