Britain's Got Talent viewers are convinced that The Phantom is a former contestant of the ITV show.
The mysterious act appeared on stage at London's Hammersmith Apollo on Thursday evening for the fourth live semi-final, but not all of the judges were impressed.
The invisible Phantom began their performance by asking judge David Walliams to think of a memory in his head and to write it down, including details such as the time it occurred.
Fellow judge Amanda Holden was then invited up onto the stage and ended up disappearing after stepping into a large box.
As David also made his way up to the stage, where there was an empty table and chairs, he was asked to look into a large mirror backstage.
Amanda suddenly appeared next to him in the mirror and recited what his chosen memory had been - but it was unclear how she knew it.
David then returned to the judging panel with a piece of paper which he was asked to read out out loud as Amanda also returned to her seat.
"David, you can't see me, you'll never see me, but I am always right here," he said as his buzzer suddenly went off and Alesha Dixon screamed.
"Until next time, goodbye," the creepy voice was heard saying as David stood up and applauded.
However, someone who wasn't clapping was head judge Simon Cowell, who said: "Am I being really stupid? As far as I was aware, Amanda got up, stood in a box, then was in the mirror, David was asked to write out what he was thinking but that part never happened."
As David explained the memory he had been thinking of, Simon still looked baffled.
The father-of-one continued: "Actually I'm not so stupid because it wasn't explained!"
After watching The Phantom's latest performance, many viewers were convinced it's actually Marc Spelmann behind the creepy voice.
One person tweeted: "I love the phantom and i really think it is marc spelmann because it keeps relating to x #BGT."
Another posted: "The Phantom is definitely Marc Spelmann, who returned a couple year later as Magician X. I'm 100% sure of it #BGT #BritainsGotTalent."
Someone else wrote: “X marks the spot” okay yeah. The Phantom is 100% Marc Spellman. I’m all for it. #BGT."
And a fourth viewer asked: "Anyone else think The Phantom is Marc Spellman aka X #BGT."
A fifth person added: "The phantom is X I’m so convinced, the delivery of this VT is just giving me Marc Spellman vibes #BGT."
Marc is a talented magician who has already appeared on BGT under two different guises in the past.
Unfortunately The Phantom didn't make it through to Sunday's final and lost out to dance group Five Star Boys.
However, Simon teased that the mysterious figure could return as a wild card.
Speaking at the end of Thursday's show, he said: "And we will now consider you as a wild card because you're obviously popular," referring to the fact that The Phantom was in the top three.
The Britain's Got Talent final airs Sunday 5 June at 7:30pm on ITV and ITV Hub.
