The 'Heart Skips A Beat' singer famously suffered embarrassment while hosting last year's series of the talent contest, when he incorrectly announced that Monica had been eliminated.
After a 2-2 vote from the judges, Olly told her: "So just to clarify, I did say we'd go to Deadlock, but unfortunately Monica you are going home I'm afraid."
His co-host Caroline Flack had to correct him, saying: "She's not, no, we're going to Deadlock."
The incident is set to be relieved on Saturday Night Takeaway this weekend, as part of the conclusion of the 'Who Shot Simon Cowell?' comedy murder mystery.
According to the Radio Times, Olly - one of the X Factor boss's many associates to end up as suspects - will mistakenly reveal himself as the culprit.
"Olly stands up and says 'Everyone, it was me!'," a source explained. "Then Caroline grabs him and says, 'No Olly, it wasn't you. Please sit down.' He sits down and apologises for making a mistake again."
Last week's penultimate episode featured a cliffhanger preview, with Dec announcing: "The votes have been counted and verified, and we can now reveal who shot Simon Cowell... you!"
Other suspects include Piers Morgan, Louis Walsh, Amanda Holden and Keith Lemon.
Earlier today it was confirmed that Dermot O'Leary will return as The X Factor's presenter this year, after Caroline and Olly announced they'd be leaving the show last month.
Saturday Night Takeaway comes to an end this Saturday at 7.00pm on ITV with a spectacular finale episode live from the show's cruise ship in Barcelona.