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.
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