The experienced English official, who has refereed top flight matches for over 20 years, traded sports to attend the 2021 Scottish Open.
But he was spotted by an eagle-eyed fan who noticed the 53-year-old fully focused on TV as he watched John Higgins defeat Noppon Saengkham 4-1, before posting a clip of the famous referee on Twitter.
Scotsman Higgins, 46, will face Ryan Day or Gao Yang next following the victory over his Thai counterpart.
Dean’s appearance in the calm and measured atmosphere of a snooker competition may have come as a shock to some fans.
The referee is known for being at the centre attention during some of football’s most intense matches where supporters have not always been the kindest towards some of his decisions.
Most notably, Everton defender Ben Godfrey appeared to stamp on Takehiro Tomiyasu’s face, while Dean and VAR official Stuart Attwell deemed it accidental.
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Sky Sports commentator Alan Smith was highly critical of the decision, saying: “You never know do you? You never know what conclusion they [referees] are going to come to.”
Tomiyasu was left bleeding from his chin while Everton came back from a goal down to win the game.
A high challenge on Arsenal defender Nuno Tavares’ ankle also went unpunished as a Richarlison goal for the Toffees was controversially deemed offside.
Dean has previously been demoted for his errors, having been temporarily dropped to the Championship in 2017 following some poor officiating during a Manchester United and Chelsea clash.