BBC News : Prosecutors in the US have charged comedian Bill Cosby with aggravated indecent assault over an alleged incident in 2004.
It is the first time Mr Cosby, 78, has been charged with any offence after months of accusations.
Andrea Constand says she was drugged then assaulted at the Philadelphia home of the former US television star.
Dozens of women have accused him of sexual assault, dating back to the 1970s, but he has denied wrongdoing.
Mr Cosby made no comment as he arrived at court to be formally charged. He did not enter a plea at the hearing where a judge set bail at $1m.
Later, his lawyer said in a statement that he would “mount a vigorous defence against this unjustified charge”.
- Single charge of aggravated indecent assault
- Incident occurred at Cosby’s home in 2004
- Victim “frozen, paralysed, unable to move”
- Charge punishable by five to 10 years behind bars and a $25,000 fine
- Will formally be charged in court on Wednesday
Earlier this month Mr Cosby opened a lawsuit against seven of the women, accusing them of defamation.
It is the second time there has been an investigation into Ms Constand’s complaint against the actor, who won acclaim for playing a family doctor and model father in The Cosby Show.
In 2005, after no charges were brought when she first made the accusation, she sued him and settled for an undisclosed sum.
He has previously said under oath he had a consensual sexual encounter with her.
How Cosby ‘drugged his victim’ – what the criminal complaint says
Mr Cosby befriended Ms Constand through her job at Temple University and she came to think of him as “a mentor and a friend” before he allegedly made two sexual advances that were rejected, said prosecutors.
Documents from her lawsuit against the star were sealed until this summer, when damaging testimony was revealed as more women came forward.
The 12-year statute of limitations was only days away from expiring, in January 2016.
Analysis by Laura Bicker, BBC News, Washington
Andrea Constand’s claims and those of dozens of other women were largely ignored by the media until recently.
It was a comedian labelling him as a rapist which made the headlines in 2014. Hannibal Buress mocked him during a stand-up routine and the recording went viral. Then came the damning deposition.
Bill Cosby was questioned under oath during a civil case brought by Andrea Constand in 2005. A judge was persuaded to unseal the document a decade after it was written. In it he admits to using drugs to dope women with whom he wanted to have sex – but insisted it was with their knowledge. He also admits to paying women to keep quiet.
More women, from the world of modelling, acting and other entertainment fields came forward, all with similar stories. For most, it is too late to bring charges – but not in in this case.
Kevin Steele, a district attorney in Montgomery County near Philadelphia, said his office had reopened the Constand case after “new information came to light”.
The prosecutors re-interviewed witnesses, examined evidence from the civil case and spoke to other alleged victims before they decided to file criminal charges, Mr Steele’s office said in a statement.
In testimony seen by the New York Times and published in July, Mr Cosby admitted he had given women a sedative, Quaaludes, when he wanted to have sex with them, but not without their knowledge.
At the height of his fame from The Cosby Show, the comedian was the highest paid entertainer on US television.