The couple have been married for 13 years after meeting on the set of 102 Dalmatians in 1999 and have two daughters together – Ella, 11, and Elsie, seven.
According to court documents obtained by Page Six Gruffudd, 47, filed for dissolution of their marriage on Monday 1 March in the Los Angeles Superior Court.
Evans, 49, wrote on Instagram: "Oh. Ok. Thanks for letting me know. I guess?"
She had previously told her 56.3k followers that they were discussing legal separation, but remained friends.
Yahoo UK has approached representatives for the couple for comment.
Last month Evans said on social media that she was in “excruciating” pain after her split from Gruffudd.
The mother-of-two revealed last month that the couple were parting after 13 years of marriage, sharing in a now deleted tweet: “Sad news. My beloved husband/soulmate of 20 years, Ioan Gruffudd, has announced he is to leave his family, starting next week.
“Me and our young daughters girls are very confused and sad. We haven't been given a reason except that he 'no longer loves me'.”
She then updated fans in an emotional post on Instagram in which she said she was “still fighting” against the break up.
Evans said has made the decision to share her break up on social media as she was struggling to cope alone.
She said: "I don’t have a mum, or a dad. I don’t have any close friends in LA. I’ve looked after my kids for half their lives alone.
"My husband knows that. We are indeed discussing legal separation, but we are still friends. You can say what you want about me being an attention seeker but you know it’s not true."
After Evans announced their split, a representative for Gruffudd released a joint statement for the couple, which said: “As you can imagine, this is an incredibly difficult time for our family and we remain committed to our children.
“Thank you for respecting our privacy.”
The couple met while starring alongside Glenn Close in Disney live action movie 102 Dalmatians and became engaged in 2006. They married in Mexico in 2007.
Gruffudd, 47, rose to fame in ITV’s historical war series Hornblower and is perhaps best known for playing Mister Fantastic in the 2005 Fantastic 4 movie.