Jane Fonda as a young girl with her mother Frances Ford Seymour.

Jane Fonda has told an audience of activists and philanthropists that her mother was sexually abused as a child before eventually committing suicide at 42.

Fonda shared the personal story at an event celebrating the 40th anniversary of the Rape Treatment Centre, which provides free treatment for sexual assault victims.

She hosted the Rape Foundation’s annual fund-raising brunch at billionaire Ron Burkle’s Greenacres estate in Beverly Hills.

Fonda said that while writing her memoirs, she reviewed her mother’s medical records and discovered she had been sexually abused when she was eight. Frances Ford Seymour committed suicide when Fonda was 12.

“The minute that I read that, everything fell into place,” Fonda said from a small stage set up in Ron’s sprawling back garden. “I knew why the promiscuity, the endless plastic surgery, the guilt, the inability to love or be intimate, and I was able to forgive her and forgive myself.”

She said sexual violence was “epidemic”, vowing: “I will support the Rape Treatment Centre for the rest of my life.”

Lily Tomlin introduced Fonda, her 9 to 5 co-star and long-time friend. David Schwimmer and Eric McCormack also spoke during the lunch, where guests included Viola Davis, Emmy Rossum and Sam Waterson.

Gail Abarbanel, founder of the Rape Treatment Centre and president of the Rape Foundation, introduced several rape survivors, including the mother of the victim of the 2012 Steubenville High School assault in Ohio. She noted her daughter’s bravery in pressing charges against her attackers – beloved star football players who had the support of the community.

Schwimmer and McCormack asked the deep-pocketed in the crowd for their support, and five people – including Burkle – spontaneously gave $100,000 to help the centre continue to offer free medical, psychological and legal services to children and adults.

The Rape Foundation also provides free training for first responders and sexual assault prevention programmes across the US.