Allison Janney says Mom producers freaked when she showed up for final season without her wig

According to Allison Janney, no one knew she's been wearing a wig for the CBS show Mom since day 1—not even the producers.

The Oscar winner told Jimmy Fallon during an interview on NBC's The Tonight Show Wednesday that her co-workers on the comedy series had a minor freak-out when she arrived on set for the final season in her natural hair.

"The producers see me like this," she says, signaling to her short, grey hair, "and they're like, 'What have you done?!' How are we gonna do…? You should have asked us before you did this to your hair?!' And I'm like, 'Guys, I've been wearing a wig since season 1, but nobody knew it.' So, everybody in the world knows about it now."

Janney told Fallon she took that Mom wig as a souvenir from the set, along with a few pairs of sweatpants because her character, Bonnie, "loved to be comfortable as does Allison Janney."

Janney previously expressed her sadness that the writers of Mom didn't have "at least another year" to "ramp up to the ending" of the show.

"We sort of found out [about the cancellation] sooner than we thought we would hear," she said. "We thought, surely, they're going to want more Mom, and they decided not. There are so many reasons behind that—most of them probably money. But, I know that [series creator] Chuck Lorre is writing the final episode and we're right now filming the third to last episode."

But now, she told Fallon, she's moving on to something completely different, a "female Dirty Harry" kind of movie called Lou.

"I've decided, Jimmy, that I'm going to go do an action-thriller movie, and I'm about to start training with a fight trainer two hours a day and learn to fight to kill," she says.

Watch her interview with Fallon above.