Now it's been reported that secretly gay A list men are worried Marcus, 26, will out them while in the house.
Marcus, who came runner-up to Little Mix in 2011, has sent a cryptic message to his famous pals.
The Daily Star reported that he warned: "I know who they are.
"I know more than a few closeted musicians in the industry and public eye who just won't talk about it. It's time for change."
Now Marcus' famous friends are said to be 'terrified', following the outspoken Scouser's cryptic warning.
And if Marcus comes across any 'closet' gay men in the house, he won't be holding back.
He continued: "It's incredibly important to have visible role models for all of us.
"I get letters from fans saying how happy they are that I was open about my sexuality on X Factor as there are not that many gay singers/performers in the UK.
"I am proud of who I am, what I am and what I am yet to achieve as an out gay man."
It was revealed last year that Marcus is in a relationship with Strictly Come Dancing star Robin Windsor, 35.