In 2011, the Scottish actor first revealed he "nearly killed" his movie co-star in a freak accident during filming, but he has refused to detail the accident until now.
MCAvoy was a guest on U.K. motoring Tv show Top Gear on Sunday night (24Feb13), and he told host Jeremy Clarkson about the terrifying incident.
He explained, "We would operate, you know when you get the motorbikes with the side car racing and you get the guy in the side doing the counter balance... We would do that for each other, taking it in turns on a golf buggy, when we made X-Men. Our golf buggy was thankfully restricted, but we got into a director's golf buggy one day unknowingly, which had been de-restricted, and I think it went the grand total of 17 miles an hour or something like that.
"I was driving, Michael was in the back doing counter-balance... hanging on. At one point it just flipped and when it sort of landed again it caught so much traction that we just launched forward. And we were going too fast because it was de-restricted. Anyway, we launched into the back of a Lexus and I flew forward, smacked my face off (sic) the windscreen and the next thing I knew I was about 15 foot away from the actual golf buggy lying on the ground.
"I looked up and Michael had somehow managed with a roof and two passenger seats... to fly forward, and he was sitting in the driver's seat and his shins were like the Niagara Falls of blood. He was just cut to shribbons (sic)."
MCAvoy showed off his driving skills on the programme's Star in a Reasonably Priced Car segment, in which celebrities drive around a racetrack, and achieved an impressive time of one minute and 43 seconds despite racing over a grassy knoll before crossing the finishing line.