LOS ANGELES • Oscar winner Ben Affleck said on Thursday that he has completed a 40-day residential alcohol rehabilitation programme, but added that battling addiction "is a lifelong and difficult struggle".

The 46-year-old, who also went to rehabilitation last year and in 2001, said in a post on his Instagram account that he remained in outpatient care and thanked his family, friends and fans for their support.

"Battling any addiction is a lifelong and difficult struggle. Because of that, one is never really in or out of treatment. It is a full-time commitment. I am fighting for myself and my family," he wrote.

Affleck has three children with actress Jennifer Garner. The couple separated in 2015, but in August, she was pictured in Los Angeles driving him to a treatment centre.

Affleck shot to fame in 1998, when he shared a Best Original Screenplay Oscar for drama Good Will Hunting (1997) with his best friend, actor Matt Damon. In 2013, he took home a second Oscar for Best Picture winner Argo (2012), which he produced and directed.

Affleck, whose prominent Batman roles were in Batman V Superman: Dawn Of Justice (2016) and Justice League (2017), has often spoken of his struggles with alcohol, which also afflicted his father and brother, actor Casey Affleck.

Casey Affleck told television show Entertainment Tonight last month that he and his brother come from a long line of alcoholics. "Ben is an addict and alcoholic. Most of my grandparents are alcoholics. My father is an alcoholic... and he's been sober for about 30 years. I've been sober for about six years," he said.

REUTERS