Ben Innes made global headlines after a picture of him with the EgyptAir hijacker surfaced last week. The image showed the 26-year-old grinning next to Seif Eddin Mustafa, who claimed to have smuggled a bomb belt on board, forcing the plane to redirect to Cyprus.
But the photograph has landed Mr Innes, from Leeds, in hot water as former students at York University claim he is a "convicted criminal".
Former students at the university, where he studied environmental science, claim they saw him attack a man during a university rugby club night out.
One witness, who did not want to be named, told The Mirror: "Ben has been hailed a champion of banter and Britishness, but he's a convicted criminal."
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According to friends, Innes was convicted of the assault outside a nightclub in York in 2009.
He was given a 12-month community order and a 12-month supervision order with a six-month electronic tag requirement.
The health and safety auditor was one of 72 passengers and crew taken hostage soon after their EgyptAir flight took off from Alexandria on Tuesday.
The snap, in which the hijacker can be seen wearing a khaki-coloured fabric belt with a series of pouches wired together, went viral after it was posted on social media.
Wearing a suicide belt - later found to have been fake - Mustafa forced the plane to re-route to Cyprus, where he proceeded to take several passengers and crew hostage and demanded to see his Cypriot ex-wife.
After a six-hour standoff, the crew along with Mr Innes and two other male foreign nationals were released moments before the hijacker gave himself up.