Mel B Sued for Defamation By Nanny Lorraine Gilles Who Claims They Had 3-Way Sex

Mel B seduced the nanny who is now suing her ... plying her with alcohol when she was just an 18-year-old foreign exchange student and had group sex with her ... this according to a new lawsuit.

Lorraine Gilles has just filed the lawsuit we told you about this morning, claiming Mel B defamed her by saying she was having an affair with Mel B's now estranged husband, Stephen Belafonte, who got her pregnant and then convinced her to have an abortion. Gilles says it's a pack of lies.

According to the suit, Gilles says Mel B portrayed her as a "homewrecker, prostitute, and extortionist, maliciously describing Gilles as being impudent, unscrupulous, and exploitive."

Gilles says in her defamation lawsuit, Mel B explained to her shortly after coming to America she and Belafonte had an open relationship. That was around the time Mel B, then 34, got her drunk and then had a 3-way with Gilles and Belafonte.

Gilles goes on to say, "at no point did Gilles and Belafonte engage in any sexual acts without Brown's knowledge or participation and at no point did Gilles and Belafonte represent to Brown that Gilles was pregnant with Belafonte's child."

Gilles says her sexual relationship with Mel B lasted 7 years.

As for sex tapes -- which Mel B claims Gilles and Belafonte used to extort her -- she says flat-out she's not in possession of any of them. Moreover, she says when they would have sex, Mel B would serve as the camera person and record the encounters and/or "take part in the menage a trois herself."