Borders cited "family concerns that require my singular focus" when announcing her abrupt resignation "with deep regret" on Monday.
But Time's Up, which campaigns against sexual assault, harassment and inequality in the workplace, has now disclosed that Borders informed members of the organization's leadership last Friday that "sexual assault allegations had been made against her son in a private forum."
"Within 24 hours, Lisa made the decision to resign as President and CEO of TIME'S UP and we agreed that it was the right decision for all parties involved," the organization said in its statement. "All of our actions were fully guided by our support for survivors [of sexual harassment and abuse]."
Statement regarding Lisa Borders' resignation pic.twitter.com/YNQdUPvSlV— TIME'S UP (@TIMESUPNOW) February 22, 2019
The attorney representing Borders' son did not immediately respond to ABC News' request for comment Friday morning.
Time's Up COO Rebecca Goldman is serving as interim CEO while the organization searches for a permanent replacement.
Prior to joining Time's Up in October, Borders served as president of the Women's National Basketball Association.
"As TIME'S UP continues to grow, I am proud of the work I have done to shepherd its continued development," Borders said in her statement Monday. "I appreciate the opportunity to support this mission and I hope my efforts will continue to resonate."
Statement from Lisa Borders and TIME’S UP pic.twitter.com/Uo7MlDb8Op— TIME'S UP (@TIMESUPNOW) February 18, 2019
Time's Up was founded in January 2018 after a number of powerful men in the entertainment industry were accused of sexual misconduct.