Mel B is to face trial for defamation.

The 43-year-old star has lost her final appeal after being sued by her former nanny, Lorraine Gilles, over claims the 'America's Got Talent' judge branded her a ''homewrecker'' and a ''prostitute'' in court papers relating to her divorce from Stephen Belafonte.

The week-long trial could cost Mel $2 million, but Los Angeles judge Dalila Lyons has encouraged the Spice Girls singer and her former employee to try and resolve the matter out of court.

A court case would likely include details of the threesomes Mel and Stephen had with Lorraine, and video evidence allegedly showing their intimate moments is available to be presented.

The ex-employee had signed a non-disclosure agreement but she will be free to take the stand and speak openly during the trial.

A source told DailyMail.com: ''Mel has been trying to keep Lorraine silent the longest, she knows more than anyone what happened Mel's marriage to Stephen.

''But now at a jury trial she can reveal everything, there's no holding back.

''Lorraine had no choice but to settle her restraining order because the legal bills were getting so high.

''But the judge said she did have the right to sue for defamation which she decided to do.

''All of Mel's appeals have now been rejected so the trial is on.

''Lorraine has a mountain of evidence to present including all the sex tapes and videos of [alleged] drug use submitted as part of Mel and Stephen's divorce battle.

''Because Lorraine was involved in that, all parties had to share all of their evidence with one another's lawyers, so she has absolutely everything.(sic)''

The 'Say You'll Be There' singer had argued to the court that she had no choice but to name Lorraine in order to get a restraining order against Stephen, but the court disagreed and sent the case to trial.

Mel appealed, but the Court of Appeal agreed with the original ruling.

It is not known when the trial will start, but the first hearing in the matter has been set for 4 February, 2019.

Lorraine, who now works as a waitress, is seeking unspecified damages and is suing for libel, invasion of privacy, and intentional infliction of emotional distress.