Actor Ben Affleck expresses discomfort as Jennifer Lopez shares intimate details in her documentary, despite his pivotal role.

He was the one who dubbed it "The Greatest Love Story Never Told." So when Ben Affleck found out that Jennifer Lopez shared his love letters with musicians working on her new album, and they nicknamed him "Pen" Affleck, he cringed.

“That seems kind of like telling it. Things that are private, I’d always felt were sacred and special. So that was a bit of an adjustment for me,” the “Batman” actor shared. Still, throughout the documentary, he’s behind the camera asking questions.

“The fact that Ben was involved at all is mind-boggling to most outsiders, but he’s doing it because it’s important to Jennifer, and he loves and supports her. As they grow older, they actually accept each other more and are less frustrated by their differences. In many ways, this is his story, too,” a source stated, adding that Ben himself has pointed out they have a different approach to their careers and are learning to compromise.

The documentary would not be the same without him. One critic dubbed Ben "the true star of the endeavor" due to his "role as muse" and praised the pair's many sweet, relatable on-screen exchanges.

Ben even admits responsibility for their first breakup in 2004, which was previously blamed on media scrutiny and cheating rumors. Jennifer Lopez confessed she was “Angry at [him] for a long time” but has “forgiven [him] all the way.”

They both rebounded notoriously quickly, with Marc Anthony and Jennifer Garner, but “it’s pretty obvious they never really got over each other,” the source said to In Touch Weekly, adding that while it may be difficult for Jennifer Garner to hear, “they’ve both moved on, and he’s made it clear how grateful he is for all that she did for him during their marriage when he hit rock bottom.”

Ben finally opens up about his demons. “The thing you discover is there isn’t enough alcohol in all the liquor stores in the world to fill up...that part of you that still feels a longing,” the “Gone Girl” actor stated of his addiction issues.

The actor’s sobriety “will always be a struggle,” the informant claimed, acknowledging that Ben has had slip-ups. “But he has made peace with his past and continues to work on his issues for the sake of his kids,” it continued.

Sam, Seraphina, and Violet are his priorities. Ben is so obsessive about protecting their privacy that he once admitted he prefers to rent a car when he meets journalists because they might “describe it and notice something I haven’t, some inelegant little smear, or get a glimpse of my daughter’s art from school, some little forgotten whatever...And maybe it hurts someone in my family.”

That is said to be greatest fear. “He firmly believes that staying out of the spotlight is healthiest for them,” the informant claimed. Luckily, Jennifer Lopez--mom to twins Max and Emme—knows when to tone it down. “The have a lot more in common than people realize, and there’s no denying they love each other deeply,” it added.

Previously, it was reported that Ben made himself “uncomfortable” by participating in Jennifer’s “The Greatest Love Story Never Told.” For those unfamiliar, the “Let’s Get Loud” songstress recently released a documentary on Prime Video about her healing journey from past traumas and her romantic relationship with Ben.

In an interview with the Daily Mail, body language expert Judi James examined the couple's gestures and on-camera chemistry. She believes Jennifer "squeezed the maximum drama out of her 'truth,'" while making Affleck appear like an "uncomfortable" child.

“Ben’s own words don’t quite synchronize with his wife’s. It has been obvious from his body language during their first romance and again now during their constant PDAs both on the red carpet and in the streets that Ben is not a huge fan of being under constant press surveillance,” Judi shared.

“During a one-to-one with the camera his body language looks uncomfortable to the point of childlike. He squints his eyes, tilts his head and clasps his hands close to his head in a ritual of what looks like coyness. His "tell" word seems to be ‘private’, while J. Lo seems to be using this documentary to spill her inner thoughts and emotions to the camera,” the body language expert continued.

Despite their differing opinions on privacy, Judi stated that Ben and Jennifer rely on one another for emotional support. “Ben is shown in the role of supporter, coach and even mentor. While she leans against his ribs as though feeding off his energy, confidence and self-belief he stands tall with chest puffed in a gesture of alpha protector and kisses her on the head. Their love story is shown as sweet but also as necessary to emotional survival. J. Lo seems to need that support and those kisses, too. Describing herself as ‘terrified,’ ‘stressed,’ ‘broken’ and even ‘older’ we are shown glimpses of her in those various states to suggest what Ben is dealing with and helping,” she explained.

Due to intense media scrutiny, Ben Affleck and Jennifer Lopez canceled their engagement in 2003. After their split, the couple moved on in their respective lives with Jennifer Garner and Marc Anthony.