Tulisa Contostavlos is suing her ex Justin Edwards for up to £100,000 over her leaked sex tape.
The N-Dubz star wants damages for breach of confidence and privacy after the seven-minute video of her performing a sex act went up on the internet.
The legal papers were served at the wannabe rap star's mother's house in West Hampstead - although Justin, who goes by the name of MC Ultra, is said to be laying low in the west country.
One of his pals told The Sun on Sunday: "He feels he can't talk publicly now because of this."
Justin's Twitter account has been flooded with abuse from Tulisa fans, but he denies that he leaked the video.
Meanwhile, Tulisa's spokesman has refuted allegations that the whole saga is a publicity stunt for the singer's new music video.
Earlier this week, Tulisa's lawyers obtained an emergency High Court injunction to ban the sex tape. The court will hear their application to extend the injunction on Monday.
> IN PICS: TULISA'S US ADVENTURE
Tulisa arrived in LA at the beginning of February to record her debut album (Pic: WENN)
And only a few days in to her trip, she was doing a Katie Price and getting her hair seen to by top US stylists (Pic: WENN)
Getting her extennos sorted. (Pic: WENN)
In between recording sessions there was enough time to hit the town. (Pic: WENN)
Tulisa was all smiles on the trip despite her recent love split from boyfriend Fazer. (Pic: WENN)
But she batted off the attention of admirers at a pre-Grammys party. (Pic: WENN)
On her way out of the studio. (Pic: WENN)
Tulisa's style offensive was also much talked about as she showed off a stylish American wardrobe. (Pic: WENN)
Tulisa is so LA now she wears sunnies in the dark. (Pic: WENN)
On Valentine's Day Tulisa headed straight out on the town after leaving the studio. (Pic: WENN)
Partying with pals, it was a case of Fazer who? (Pic: Twitter)
Never far from her side was her PA and best mate Gareth Varey who also had a tattoo of her name done in his leg during their trip. (Pic: WENN)
And bumped into former <em>TOWIE</em> star Mark Wright. (Pic: Twitter)
With debut single <em>We Are Young</em> in the can, it was time to film the video. (Pic: Splash)
That's a lot of luggage there dear! (Pic: Splash)
Getting cheeky on the shoot. (Pic: Splash)
And of course Gareth had to get in on the action in the video as Tulisa showed off her curves in a swimsuit. (Pic: WENN)