The ladies also tell ET what it was like co-starring with Dakota Johnson's father, Don, in 'Book Club.'
ET recently caught up with the ladies at CinemaCon in Las Vegas, Nevada, where they were promoting their new movie, Book Club. Naturally, we had to ask them which novels were on their personal reading list.
Book Club also stars Don Johnson, the father of Fifty Shades of Grey star Dakota Johnson. Fonda and Keaton both admitted they've dived into the erotic romance novels, penned by E. L. James, that the movie franchise is based on.
"I think I'm the only one here that actually read it from beginning to end," Fonda told ET's Kevin Frazier. "But it was way before I knew about the movie. I was just curious to see why everybody was talking about it."
Keaton chimed in, saying, "It was way before the movie, we must take note of that. Jane, what were you doing reading that?" to which Fonda responded, "On my own, I did it on my own."
"I like the romance of it," Fonda added. "I like the fact that he [Christian Grey] actually fell in love with her [Anastasia Steele]. I thought that was cool."
Fonda and Keaton's other Book Club co-stars, Candice Bergen and Mary Steenburgen, also confessed they've read the Fifty Shades book series, though Fonda joked they've only read "the dirty parts."
"I read the dirty bits and I admit that," Steenburgen revealed.
"I read it. I started to read it, and then the [woman] who runs our house asked if she can borrow it and I never saw the book again," Bergen added. "I was too embarrassed to go to the bookstore and get another copy, so she owes me the copy."
Book Club hits theaters on May 19. Watch the video below to hear more from the upcoming comedy!