Jacqueline Kennedy Onassis thought boyfriend Warren Beatty’s skills as a lover were just mediocre, a new book claims.

“Oh, he’s fine. Men can only do so much, anyway,” the former first lady once said, according to an excerpt of “Jackie: Public, Private, Secret” obtained by People Wednesday.

Onassis, who died from non-Hodgkin’s lymphoma in 1994, briefly dated Beatty, 86, in the mid-’70s after President John F. Kennedy’s death.

According to author J. Randy Taraborrelli, the late socialite met the movie star when she was working as a book editor and trying to “woo big names” for memoirs.

Onassis reportedly found Beatty “interesting” at first and so they went on a few dates, including one that ended with him spending the night at her Fifth Avenue home.

However, the dalliance ended a few months later because the philanthropist thought the “Bonnie and Clyde” star — who was considered a “Casanova” at the time — was “self-absorbed,” per Taraborrelli.

Onassis reportedly felt Beatty was “consumed by his own career and movies” and “all he wanted to do was talk about directors and producers and films, and she just wasn’t into any of that.”

By the end of the relationship, the mother of two reportedly thought it had lasted “two weeks longer than it should have.”

For more Page Six you love …

A rep for Beatty did not immediately return Page Six’s request for comment on the book.

However, this is not the first time the “Bugsy” star’s love affair with Onassis has been publicized.

The romance was also discussed in “Jacqueline Kennedy Onassis: A Life Beyond Her Wildest Dreams,” which was released in 2014.

Beatty, who has been married to actress Annette Bening since 1994, does not appear to have ever commented on Onassis.