It’s the tightness around her lips, the glassiness of her eyes and the way her eye makeup smears as she fights back tears.

When Constance Zimmer breaks down in the final episode of FX’s “Love Story: John F. Kennedy Jr. and Carolyn Bessette,” every inch of her face exudes that painful mix of sorrow and fury that often accompanies grief.

Zimmer soars in Episode 9, “Search and Recovery,” as her character, Ann Marie Messina, deals with the cruel shock of losing both of her daughters in the plane crash that also killed JFK Jr. Zimmer worked hard to capture the aggravation that Ann feels — including the smothering effect of the fame and notoriety that envelops the Kennedys, which is one of the central themes of “Love Story.”

“I’ve never poured more of myself and my own trauma and grief into a character in order to make it feel so raw,” Zimmer tells Variety. “I didn’t care about what I looked like. I just cared about giving people who deal with grief every day a space to cry. I really wanted people to have it. It felt like it was something we all need.”

The most powerful scene, which runs eight minutes, comes when Ann unexpectedly runs into Caroline Kennedy (Grace Gummer), at the apartment of Kennedy Jr. and Bessette after the tragic crash. Ann palpitates with anger and starts to tell Caroline how devastating it is to see Lauren, in particular, reduced to a footnote in the overall tragedy.

“Maybe it’s best I go,” Caroline gingerly offers in the episode penned by Connor Hines and Elizabeth Beller and directed by Anthony Hemingway. Ann responds, “I’m not finished — and I will not be dismissed a second time.” Her tone that makes Caroline sit down at the far end of a long wooden dining table.

Zimmer stresses that she threw herself into the role out of respect for families caught up in the whirlwind of a violent death. She also saw Ann as a rare opportunity to portray a woman of a certain age who defies stereotypes.

“I felt that this was going to be a woman that was not going to shy away from any morsel of letting somebody understand what her grief was. I just leaned really hard into that,” Zimmer says.

The actress didn’t have much background material on Ann, who worked as an elementary school teacher in Connecticut and died at age 67 in 2007.

“To embody her essence was really all I cared about. Everything I read about her was that she was just an incredibly caring person. It felt like something I needed to really, really get right,” Zimmer says. “I was representing the non-celebrity, the person that wasn’t into the fame of it all. She just wanted to make sure her children were going to be OK. And when they weren’t, it was devastating.”

Zimmer has been gratified by the strong feedback she’s received from a few people who knew Ann, including former students. As a seasoned thespian who has logged dozens of guest roles as well as series regular gigs ranging from CBS’ “Joan of Arcadia” to Lifetime’s “UnReal,” Zimmer is bowled over by the critical raves that “Love Story” has received.

From her vast experience on sets, she knew that the series would be very good, but she had no idea if it would find an audience. She certainly didn’t expect it to unleash a wave of 1990s nostalgia and mania among Gen Alphas to learn more about the Bessette sisters.

“Everybody who worked on this show really cared, and you don’t get that very often. They really cared about creating the characters and doing everybody justice,” Zimmer says. “From the second you walked on set, everybody knew how much this story meant to different people all over the world. The fact that it’s been so incredibly embraced with such love is like the greatest gift any of us who worked on it could have been given.”