The former X Factor judge and daughter Kelly Osbourne joined Jonathan Ross, Rita Ora and Davina McCall on the judging panel of the ITV singing talent show on Saturday night, filling in for comedian Ken Jeong.
Kelly, 35, was adamant the celebrity masquerading as Unicorn is Scissor Sisters frontman Jake Shears after he sang Blur’s Girls and Boys in a British accent, which threw viewers and the other judges.
She said: “I really do think I know who you are. I think it’s Jake Shears from the Scissor Sisters because I know that my dad has seen him naked, was it...
Mum Sharon, 67, interjected: “Elton’s stag party yes!”
Unicorn had previously revealed as a clue to his identity that Black Sabbath rocker Ozzy Osbourne, 71 had seen him naked.
Judge Rita Ora said: “I’m going to stick with [actor] Matthew Morrison because there were a lot of Glee references.”
Sharon exclaimed: “I hope Matthew was’t naked in front of my husband!”
Elton John, 72, has married husband David Furnish, 57, twice - first in a civil partnership in 2005 and again when gay marriage became legal in 2014. He and Jake Shears, 41, are known to be close friends.
After being unmasked later on the show Shears confirmed: “I was at Elton’s stag do, and I was on a pole...”
Meanwhile, Ora, 29, was left redfaced after being outfoxed by BBC Radio DJ Sara Cox’s name.
Ora told Fox: “I know your voice, maybe you’re on the radio because you sang On My Radio before... You’re Sara Fox! I’ve got it.”
Fellow judge Jonathan Ross exclaimed: “If any of us knew who that was!”
Ora replied: “She’s a radio DJ,” to which host Joel Dommett added: “Do you mean Sara Cox?”
Ora looked embarrassed and admitted: “Oh yeah! I got distracted ‘cause I’m looking at a fox!”
So far The Masked Singer has seen EastEnders actress Patsy Palmer, former Home Secretary Alan Johnson, former England footballer Teddy Sheringham and singer Kelis revealed as the secret celebrities hiding inside Butterfly, Pharaoh, Tree and Daisy.
The Masked Singer continues weekly on ITV on Saturday nights.