Footage of a blonde-haired female performing oral sex on an unidentified male was released earlier this week.
The X Factor judge has now confirmed that it is indeed her in the tape in a new clip released on YouTube, and identified the man in the video as her ex-boyfriend Justin Edwards, otherwise known grime artist MC Ultra.
"I wanted to set the record straight on a certain tape circulating online, that consists of footage of me and my ex-boyfriend having an intimate moment," she said in the video.
"I have never been the type to sit down and keep my mouth shut, and to keep quiet about anything, especially when I've done nothing wrong whatsoever."
Showing a photo of Edwards, she says: "Justin is someone I was seeing from the age of 17 on and off for many years. By the time I was 19, we were together for a year and a half, I practically moved in with him and I loved him deeply. We talked about marriage, we talked about kids."
Contostavlos then reveals that she was aware of a possible tape last year when Edwards threatened to release the clip online.
"Six months ago, I got a call from a mutual friend saying that apparently he has footage of me, that he's been threatening to bring it out to ruin my career," she continued.
"I confronted him, he lied about it. And here we are today and the footage is now circulating online.
"As you can imagine, I am devastated, heartbroken. When you share an intimate moment with someone that you love and care about and trust, you never imagine that footage will be shared with the world."
She added that she wanted to share her side of the story and to name Edwards as the man who released the video.
"I don't feel that I should be the one to take heat or stick," she went on to say. "This is something that he took upon himself to put online. He's now sitting in silence, saying it's not him on the tape, when it is.
"I have been deeply betrayed by him. This is something I've had to deal with, there's nothing I can do about it, but I do feel that I should share my side of the story."
The N-Dubz singer added: "When you judge someone, it doesn't define the person you're judging, it defines you."
Finally, she thanked her supporters, saying: "Lots of love to my fans, I apologise to anyone that this has offended. I know for a fact it will not happen again."
Edwards has since taken to Twitter to write: "I believe in silence being a sign of Integrity but in this case I guess I'll have to speak up and Lay out the facts and let you guys decide.
"To find the truth both sides of the story should be heard b4 (sic) passing judgement #thatisall"
He had previously tweeted on March 19: "I didn't wanna say anything on the subject but I see peoples imagination running away.. it's nothing to do with me.#backtowork
"Keepin my twitter quiet outta respect for a certain someone no other reason than that."
Contostavlos obtained a court injunction against the tape earlier this week after its release online.
A post on Dappy's Twitter account had previously alleged that the male in the video was their N-Dubz bandmate Fazer.
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