Rob Lowe arrives at the Brothers & Sisters: The Complete First Season DVD Launch Event on September 10, 2007 in Los Angeles, California.
Jeffrey Mayer/Jeffrey Mayer

Rob Lowe is "very upset" about accusations of sexual misconduct by his former nanny, his Brothers & Sisters co-star Ron Rifkin told Usmagazine.com.

"It's a horrible situation," Rifkin said at a benefit for the Scleroderma Research Foundation in Beverly Hills Wednesday.

"He is the greatest," Rifkin told Us. "He can take care of himself."

In a law suit filed Monday, Lowe's former nanny claims that he regularly exposed himself during the seven years she worked on and off with his family.

Jessica Gibson, 24, quit her job in February. She alleges the 44-year-old actor also groped her butt and "placed his hand" inside her pants several times between September 2005 and January 2008.

Click here to watch Gibson's appearance on the Today show.

Before the allegations were made public, Lowe published a blog on the Huffington Post last week claiming that he was being blackmailed by a former employee for $1.5 million in "hush money."

"My family is devastated at this betrayal," he wrote. "This woman worked in our home and traveled with us off and on for seven years, without complaint."

Lowe and his wife Sheryl are suing the nanny for allegedly spreading malicious lies about them.

Should Katie Couric Stay or Go?