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For years Casey Affleck, Ben’s better-looking brother, has had a career in his elder sibling’s shadow. It has meant, he notes, that he has been able to observe people afflicted by fame, as his brother has been, and watch them make mistakes.

“The process seems similar to being thrown to the sharks and being eaten,” he says. “So it was good I never went that way and good that Ben could save himself by directing Gone Baby Gone. Nobody knew if he was going to be any good or not, and people have really been surprised at how good he is.”

Casey plays the lead, the private investigator Patrick Kenzie, who works with people who “fall through the cracks”. Michelle Monaghan, Morgan Freeman and Ed Harris co-star.“It was easy working together [with Ben] because we both speak our minds plainly. I think my only difficulty was that Ben wanted to make a more commercial movie than I am used to. He has a pretty good idea of what the audience wants and I very rarely approach a performance thinking of what the audience wants. I am still a bit of an unbroken horse in that field.”

Until recently Casey Affleck has been the vaguely familiar face behind the leading actors in films such as the Ocean’s Eleven series (as the getaway car driver Virgil Malloy). Then he played Robert Ford in Andrew Dominik’s The Assassination of Jesse James by the Coward Robert Ford opposite Brad Pitt and award nominations, including one for Supporting Actor at the Oscars, rolled in.

“Man, is it nice to be acknowledged! It felt like my career had been going through a desert and suddenly I arrived at a feast. Two major parts in two fantastic films. It was just dumb luck.”

Affleck Jr, 32, is dark with calm blue eyes and lacks his brother’s shovel chin. He seems decorously proper rather than cool. First seen in 1995 in To Die For, in which Nicole Kidman recruited him to assassinate Matt Dillon, Affleck notched up his 20th film with Gone Baby Gone. Others on his CV include Good Will Hunting, Chasing Amy – both alongside his brother – and The Last Kiss.

He grew up mainly in and around Boston. “We shot Gone Baby Gone on the seamy side of Boston. Being quite close to home, I didn’t have to pick up the local accent and how people relate to each other there, and our mom used to come to the set with lunch. Sometimes we still felt like a couple of kids.”

His mother, a teacher, raised him and Ben, 35, by herself after their father drifted out of the picture. Childhood was itinerant, and the boys started acting young as their father had been involved in the Theatre Company of Boston and their mother’s best friend was a casting director. He went on to study physics, astronomy and Western philosophy at Columbia University, New York, but dropped out, as Ben had done before him, to act.

He is married to actress Summer Phoenix, sister of the late River Phoenix and Affleck’s buddy Joaquin. They met in London in 2000 when she was playing the title role in the East End-based film Esther Khan for director Arnaud Desplechin.

“My next job,” he says in that decorous way of his, “is an animated family film that I co-wrote called Aardvark Art’s Ark.” He pauses, smiles again. “Small and interesting. That’s good!”

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