Jessica Alba struggled to look tough while filming a gun scene for new TV series L.A.'s Finest because she had no idea what she was doing.

The Sin City actress co-stars in the police drama with Gabrielle Union, who reprises her role as Sydney Burnett - the character she played in the action movie Bad Boys II - for the franchise spin-off.

Jessica was cast as Burnett's cop partner in early 2018, but instead of easing herself back into acting after taking time out to focus on her baby and household product brand The Honest Company, the mother-of-three found herself thrown in at the deep end.

"It was literally torture...," she cringed as she recalled filming one particular action scene.

"First of all, I'm not really like, a gun person, and then I had to learn how to do it in like, 10 minutes, and I'm trying to learn all the lines," she told U.S. morning show Live with Kelly and Ryan. "And I kinda took a break from acting because I started a company, and so I'm just trying to get warm, get used to being on a set and saying words, and all of that, and they give me this long monologue while I'm putting together an AK-47 (assault rifle), and it was really hard!"

Despite the challenges Jessica faced, she had a blast being back on set, because she had really missed flexing her acting muscles.

"I got to go back and jump in and partner up with Gabrielle Union, and she created the show," the star said.

She also had a little sibling support as her brother, actor Joshua Alba, was cast as her onscreen relative.

"My brother actually plays my brother on L.A.'s Finest!" Jessica beamed.

L.A.'s Finest debuted on U.S. cable provider Spectrum on Monday night (13May19).