The 27-year-old singer - who was previously believed to be romancing show stylist Grace Woodward - was reportedly told by record bosses he had to keep his fledging relationship with backing dancer Sarah Robinson under wraps to prevent him from losing female fans.
However, the loved-up pair have now been secretly dating for three months.
When asked whether he is still single, he said: "I'm sorry, I can't say that. I can't promise that."
An 'X Factor' insider added to The Sun newspaper: "Sarah and Matt had a code word so they didn't get rumbled. She was worried it wouldn't last because of his career but three months on and it's getting stronger."
Matt and Sarah reportedly met just weeks after the 24-year-old dancer parted ways from her boyfriend of four years, Blair Dreelan, who auditioned for 'The X Factor' three times alongside boyband 4th Ba5e but never made it.
The source added: "It seems Sarah swapped an 'X Factor' loser for an 'X Factor' winner. But it's not that simple - with Matt it's the real deal."
Matt recently admitted taking part in the talent competition "saved" him from his former rebellious life.
He said: "Entering 'The X Factor' changed my life. It's saved me, in a way. I was a rebel, drifting about having a laugh and a drink with mates. I never went mental but I was stupid."