London - Robin Williams reportedly fell off the wagon while making 'The Crazy Ones'.
The late 63-year-old actor - who got sober in 1983 before relapsing briefly in 2003 - stunned cast and crew members on the CBS show when he insisted on drinking real alcohol when filming a scene at Beverly Hills restaurant Spago last May.
A source told the New York Post newspaper's Page Six column: "Robin insisted on a real drink. No one had seen him drinking before this. One drink led to another, but it seemed to calm him down."
According to the insider, Robin - who checked into rehab in June to "maintain his sobriety" - was said to frequently infuriate his co-stars on the show because he often went off script, forcing the likes of Sarah Michelle Gellar to have to improvise their responses.
He also complained he "had a bad feeling" about the lack of chemistry on the set of the show, which was cancelled after just one season, and spent most of his downtime with his beloved Pug Leonard.
The source said: "He brought it everywhere with him. When he wasn't filming a scene, he was holding and petting and fawning over the dog."
It was recently revealed that Robin - who was found hanged at his California home on Monday - had attended an Alcoholics Anonymous (AA) meeting shortly before he died.
Comedian and fellow AA member Argus Hamilton said: "He was at a meeting on Saturday. He had got out of rehab and was sober at the meeting." - BANG Showbiz