Colin Farrell almost quit acting in 2004.

The Irish actor was horrified with the savage reviews his performance in 2004's epic blockbuster 'Alexander' - in which he starred alongside Angelina Jolie - received and admits it made him doubt his abilities as a performer.

He said: "That was tough. I say tough, relative to a Charmed life, but I'm not going to apologise for how much it affected me emotionally and psychologically.

"I was going to walk away from acting. I couldn't even buy a packet of cigarettes without feeling I needed to say sorry to the guy behind the counter just in case he happened to see the thing."

The 34-year-old star - who has sons James, seven, and Henry, 14 months, from previous relationships - continued to make movies, but admitted his partying ways got so out of control, he was embarrassed by his behaviour on the set of 2006's 'Miami Vice'.

He recalled to the Daily Mirror newspaper: "I just completely fell to s**t on that one. It was literally the first time I couldn't say to anyone around me, 'Have I been late for work, have I missed any days, have I been hitting my marks?' Because the answers would have been yes, yes, and no."

Once the film wrapped, Colin - who has now been sober for over two years - checked into rehab because he felt he needed support to get himself back on track.

He admitted: "I lost the ability to be confident that I could make a change myself."