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A former British heavyweight boxer, who once fought Mike Tyson, knocked out a troublemaker with one punch.

Julius Francis, a former British heavyweight boxer, is now working as a security guard at a sports complex.

Francis, 57, was working security at London's BOXPARK Wembley when the unruly man began arguing with other security staff.

The man, wearing a blue durag, argued with the security members and shoved the shortest man on the security team.

As other security officers tried to deescalate the situation, Francis worked his way around the barricades to the open sidewalk.

As the man approached him and raised his hand, Francis knocked him out cold with one punch.

Video of the punch went viral on Twitter.

BOXPARK founder and CEO Roger Wade defended his employee in a message on social media. He added the hashtag #istandwithjulius.