Bill Cosby called himself a “sick man” and apologised to the mother of his alleged victim, a Pennsylvania court heard.

Gianna Constand told the jury that her daughter Andrea Constand's behaviour had changed after the alleged assault, and recounted a two-hour phone conversation she claimed to have had with the legendary comedian about the incident.

She said that her daughter moved home after the alleged assault, but did not immediately tell her parents what had happened. Instead, they began to notice subtle changes in her behaviour.

“She was having a lot of nightmares,” Ms Constand told jurors at the Montgomery County Courthouse in Norristown, adding: "It was very, very frequent that she would scream in her sleep or she would wake up in a sweat.”

Her daughter, 44, also developed a twitch in her eye, and a habit of staring off into space, she said. Her daughter had become “more nervous” than she had been before, she added.

Eventually, her daughter broke down and told her what had happened in a phone call on her way to work, she said.

“She said, ‘Mom, I think I’ve got PTSD,’” Ms Constand recalled, her voice shaking. “She said, ‘Mom, he drugged me and he raped me.’”

When she returned home from work, Ms Constand says, her “motherly instincts” kicked in. She demanded Mr Cosby’s phone number, and called the comedian to confront him. When he eventually called back, she says, they engaged in a more than two-hour phone conversation.

Bill Cosby: Career in pictures Show all 20 1 /20 Bill Cosby: Career in pictures Bill Cosby: Career in pictures Bill Cosby Winner of his first Emmy for 'I Spy' is Bill Cosby being congratulated by his wife Camille held at Americana Hotel, 1966 Bill Cosby: Career in pictures Bill Cosby Bill Cosby in 'I Spy', 1960s Bill Cosby: Career in pictures Bill Cosby Bill Cosby in July 1973 in Perth Bill Cosby: Career in pictures Bill Cosby Bill Cosby and Richard Pryor in 'California Suite', 1978 Bill Cosby: Career in pictures Bill Cosby Bill Cosby and Elmo in Sesame Street, 1989 Bill Cosby: Career in pictures Bill Cosby Bill Cosby poses for a picture with Florence Griffith-Joyner in June 1989 Bill Cosby: Career in pictures Bill Cosby Comedian Bill Cosby back in 1992 Rex Features Bill Cosby: Career in pictures Bill Cosby A scene from a 1992 episode of 'The Cosby Show' AP Bill Cosby: Career in pictures Bill Cosby US Monica Seles breaks into laughter as she jokes with comedian Bill Cosby during a celebrity match in the stadium at the US Open for the Arthur Ashe AIDS Challenge on 27 August 1995 Bill Cosby: Career in pictures Bill Cosby Bill Cosby meets Toronto Blue Jays' All-Star Joe Carter after the Stars played the Stripes in the Celebrity All-Star game which preceded workouts for the 67th All-Star Game at Veterans Stadium on 8 July 1996 in Philadephia Bill Cosby: Career in pictures Bill Cosby Co-hosts Oprah Winfrey and Bill Cosby joke with each other during the opening of the 2000 Essence Awards 14 April 2000 at Radio City Music Hall in New York City Bill Cosby: Career in pictures Bill Cosby Bill Cosby jokes with baseball great Hank Aaron after they both received the Presidential Medal of Freedom Award from U.S. President George W. Bush during a ceremony on 9 July 2002 at the White House in Washington Bill Cosby: Career in pictures Bill Cosby Bill Cosby poses backstage after winning the 'Bob Hope Humanitarian Award' during the 55th Annual Primetime Emmy Awards at the Shrine Auditorium on 21 September 2003 in Los Angeles Bill Cosby: Career in pictures Bill Cosby 'Tonight Show' host Jay Leno and comedian Bill Cosby laugh during a surprise visit by Cosby to sign a Harley-Davidson motorcycle that Leno is using to raise money for the victims of Hurricane Katrina at NBC studios on 9 September 2005 in Burbank, California Bill Cosby: Career in pictures Bill Cosby Bill Cosby speaks during a taping of 'Meet the Press' at the NBC studios on 14 October 2007 in Washington Bill Cosby: Career in pictures Bill Cosby Bill Cosby at the 12th annual Mark Twain Prize for American Humor at the John F. Kennedy Center on 26 October 2009 in Washington Bill Cosby: Career in pictures Bill Cosby Bill Cosby speaks at the National Action Network's 20th annual Keepers of the Dream Awards gala in New York on 6 April 2011 Reuters Bill Cosby: Career in pictures Bill Cosby Bill Cosby during the 100th anniversary celebration of the Beverly Hills Hotel & Bungalows supporting the Motion Picture & Television Fund and the American Comedy Fund, 2012 Getty Images Bill Cosby: Career in pictures Bill Cosby Bill Cosby speaks onstage at the Thurgood Marshall College Fund 25th Awards Gala on 11 November 2013 in Washington Bill Cosby: Career in pictures Bill Cosby Bill Cosby performs at the Treasure Island Hotel & Casino on 26 September 2014 in Las Vegas

After learning what had happened to her daughter she was "distraught", she said.

"They were good friends. She viewed him like a father. He is 10 years older than even her own father," she testified, breaking down on the stand.

She then confronted Mr Cosby, 79, by phone during the two-hour call in which she said he "surrendered" to her about the sexual encounter and told her about how he had touched her daughter’s breasts and “digitally penetrated” her.

At one point in the call, he referred to himself as a “sick man”, she said.

“He said, ‘I apologise to Andrea.’” Ms Constand testified. “He said, ‘And I apologise to you mom.’” She said Mr Cosby referred to her as “mom” throughout the conversation.

Asked if she regretted anything about the conversation, Ms Constand said only: “‘I wish that I had recorded it.”

After that conversation, she said, she bought a recording device in the hope that Cosby would again confess to harming her daughter. But she said he kept their next conversation short.

Prosecutors played a recording of the call, in which Mr Cosby offered to pay for Constand's education.

"She could go to school," he said. "If she wanted to do that, then I would be willing to ... pay for the schooling.

Mr Cosby is currently facing three counts of aggravated indecent assault, stemming from an encounter with Ms Constand at his Pennsylvania home in 2004.

The former basketball coach claims the comedian drugged and molested her after a private dinner at his house. Though Mr Cosby has acknowledged having a sexual encounter with Ms Constant, he maintains it was consensual and has pleaded not guilty.

His defence pointed out that at no point in the phone conversation with Ms Constand's mother did Mr Cosby admit to sexually assaulting her.

Mr Cosby’s defence has rested largely on painting his encounter with the younger Ms Constand as consensual, and their relationship as “romantic”.

Defence attorneys have commented on the multiple times that Ms Constand visited Mr Cosby at his residence, and one instance in which she visited his hotel suite alone.

But the elder Ms Constand took a similar line to her daughter, who had earlier testified that she viewed Mr Cosby as a mentor and not a lover.

“Cosby had mentored her, and they were they were goods friends. She viewed him like a father,” Ms Constand said, adding: “He betrayed her.”

Some 60 women have come forward to say Cosby sexually violated them, all but destroying his nice-guy image, but the statute of limitations for prosecution had run out in nearly every case.

Constand's case is the only one in which Cosby has been charged. Cosby potentially faces up to 10 years in prison on each of three related aggravated indecent assault charges, although the sentences could be merged, and he could get far less time if convicted.