The victim alleges she went to the singer's house after a concert at a nightclub - and was assaulted by rapper Lowell Grissom Jr - aka Young Lo.

The woman's lawyer called it "one of the most horrific cases" she had seen.

Newsbeat has contacted Chris Brown's representatives for a comment. We've been unable to contact a representative for Young Lo.

A lawsuit was filed at the Los Angeles County Superior Court on Wednesday.

It alleges the woman, known only as Jane Doe, went to 1 Oak nightclub on 23 February last year.

"At some point our client was invited to attend an 'after party' at a recording studio to meet Young Lo and Chris Brown," lawyer Gloria Allred said at a press conference.

Gloria Allred read out details of the lawsuit to journalists on Wednesday

The lawsuit alleges the woman's phone was taken away from her and when she asked to leave she was told she couldn't have it back as the party was moving to Chris Brown's home.

It claims the singer provided alcohol and illegal drugs and was also seen with guns in front of guests at his home.

"The lawsuit alleges that while she was at Brown's house the plaintiff became the victim of horrific sexual assault," Ms Allred said.

It claims the woman was raped by Young Lo and sexually assaulted by another woman.

The lawsuit accuses Chris Brown and others of several allegations including sexual battery, assault and gender violence - and says the victim is seeking damages.

"This is one of the most horrific sexual assault cases that I have ever seen," said Ms Allred.

"Our client Jane Doe has been severely traumatised by what she was forced to suffer."