Allison Janney is overjoyed she can rave about Mom co-star Anna Faris' engagement at last, after having to keep the news "very quiet" for months.

Rumours swirled in November (19) that the actress was engaged to cinematographer Michael Barrett, after she was spotted sporting a diamond ring. And days later, Faris appeared to confirm the story when she was filmed saying "Thank you" after a photographer congratulated her on being a bride to be.

Now, Janney has revealed she and Faris marked the happy news long ago.

"I know she's been engaged for a long time," Janney tells Us Weekly. "I kept it very quiet, I'll have you know! So, I celebrated with them a long time ago."

She added that the Overboard star, 43, didn't make a big fuss about showing off her new sparkler, but it was hard to miss.

"I didn't know he (Michael) was going to propose, but I saw the ring one day," she shares. "I went into her room to work on lines (for the show), and then I was like, 'What is that ring on your finger?' ...I think she was waiting for everyone to notice. 'Oh, that's it,' and then ... yeah, it was fun."

Faris has been dating Barrett since late 2017. She was previously married to Ben Indra from 2004 to 2008, and to Guardians of the Galaxy star Chris Pratt from 2009 to 2018. They share seven-year-old son, Jack.

Pratt has since remarried - he wed Arnold Schwarzenegger's daughter Katherine in June (19) after a whirlwind romance.