Sitting in the first few rows, the gentlemen - later identified as Danny McAfee, a singer in a Dundee Led Zeppelin tribute band - first became visible when the man beside him asked a question.
Immediately, social media exploded into life.
@tyler_durdenkds asked: “I didn’t hear a word of that question, what was the guy with the fake moustache about beside him?”
@mickmcavoy accurately predicted: “I suspect moustache may soon trend across Scotland.”
He wasn’t wrong. Before long everyone seemed to be weighing in with jokes about the usual sighting.
Scottish singer Amy MacDonald tweeted: “Please can we just wrap this up and hear from #fakemoustacheguy it’s what the people want. #ScotDebates”
Green Party MSP Patrick Harvie clarified: Can I just put all the speculation to rest - I was NOT moustache guy.”
While @BrianSpanner1 added: “So all it took to break the concentration of the new politically engaged Scottish electorate was a ten bob fake moustache.”
There then followed a scramble from the news outlets to identify the man who, once found, was more than happy to oblige and reveal his motivations.
Speaking to Buzzfeed, Mr McAfee said: “I thought it was going to be a yawnfest, so I brought along this moustache to brighten it up a bit – it was to give my mates at home a laugh really, and I have a bucket of missed calls so I think it worked.
“[Sturgeon] was great tonight, I thought the debate was pretty boring but she was very good,”
The moustache was visible in another couple of shots before it was removed after an ad break, with it later emerging Mr McAfee had been asked to take it off.
Still, the short time it was glued onto his top lip was enough to make a lasting impact.
SNP candidate Pete Wishart said: “We will remember that simply as the ‘Moustache Debate’.”
SCOTSMAN TABLET AND MOBILE APPS