The 15-year-old wannabe singer from Fitzroy, who was eliminated from the Australian version of the reality television competition two weeks ago, said that he and 17-year-old Carmen recently split up.
According to the Herald Sun, Sykes said that he had been the one to end the relationship with his fellow Fitzroy High student.
Sykes, who was diagnosed with Asperger's syndrome five years ago, revealed that he has had lots of negative comments from people since his time on the show, but has said that he just ignores them.
"It's pretty clear I was the weird and awkward one on the show," he said. "The haters are going to hate. You are always going to get people who say those things just because they can, it's just how society works.
"I walk down the street and you get the dudes in hoodies who bag you out. You get it, you've just got to move on."
Sykes' fellow X Factor contestant Mitchell Calloway was accused of bullying Sykes on the show, but his mother said that their relationship was "fine", adding: "Boys will be boys."
> Australian 'X Factor' 2011 winner announced
Watch Declan Sykes perform on The X Factor below: