Ben Affleck has dropped a ton of weight since Jennifer Lopez‘s divorce filing, despite his fast food comfort binges, and it’s got him putting together a plan to bulk up – starting first with his pancake butt!

“Ben’s always had this Achilles heel when it comes to his workouts – he keeps up with his cardio and lifts weights at home to keep his upper body tight, mainly because he’s so afraid of letting his pecs turn saggy and developing man boobs,” an insider exclusively tells In Touch. “But squatting and leg work isn’t his deal at all. He hates it. So, the butt’s droopy as a result and Ben’s kind of buried his head in the sand about the problem until now.”

However, the source notes that the Gone Girl actor, 52, is “changing his mind about it now ” because the “divorce has him wanting to really buff up and get into the best possible shape – especially now that he’s back on the dating scene.”

“So, the trainer’s coming in, the junk’s being phased out, as are the cigarettes, and fixing his rear end is physical priority number one! He may opt for some new tattoos at some point soon, too, but that’s another story,” the insider says.

Ben Affleck Getting in Shape While ‘Back on the Dating Scene’ (EXCL)
In May, In Touch exclusively broke the news that Ben and J. Lo, 55, were “headed for a divorce” as they neared their second wedding anniversary.

Throughout the summer, the A-listers added fuel to the divorce fire as both proceeded to leave the house without wearing their wedding rings. Not to mention, Ben didn’t participate in his longtime lover’s big red carpet events. That said, the pair came together for their kids, as the “On the Floor” singer was in attendance for the high school graduation of Ben’s eldest daughter, Violet Affleck, whom he shares with ex-wife Jennifer Garner.

The timing of their marital woes didn’t line up with their career collaborations, like the film Unstoppable, which premiered at the Toronto International Film Festival on September 6. J. Lo stars in the movie that is produced by Ben and Matt Damon’s production company, Artists Equity.

“Unstoppable is a tricky one because Ben and Matt are so invested in its success, even if everything you see indicates that Ben and Jennifer are ending their marriage,” a second source exclusively told In Touch in a story published on August 8.

Insider No. 2 later added, “Right now, Ben plans to support the movie, no matter what’s going on with him and Jennifer. They are business people first, and they’re both committed to supporting this film, even if they’re not committed to their marriage.”

J. Lo filed for divorce from Ben on August 20, In Touch confirmed at the time. In the filing, the Enough actress listed April 26 as their official date of separation.

The pair has yet to publicly comment on their divorce.

On September 6, J. Lo made her first red carpet appearance after filing for divorce at the Unstoppable premiere at TIFF. The multi-hyphenate donned a sexy revenge dress that exposed major skin.

Ben may have skipped the premiere, but Matt attended the big night and even had a “deep” conversation with Jennifer.

One day after the event, a source told People that Jennifer and Matt “laughed and spoke more seriously, and for several minutes, they clasped hands as they spoke.”