Peter Facinelli Files for Divorce from Jennie Garth

It was only a matter of time ... but Peter Facinelli has finally filed divorce papers in an effort to end his marriage to Jennie Garth.

According to the docs, filed moments ago at L.A. County Superior Court, Facinelli cites "irreconcilable differences" for the split. Facinelli also wants joint physical and legal custody for their 3 minor daughters.

Interesting timing -- considering the two were spotted out shopping together in L.A. just this weekend.

In the docs, filed by Facinelli's attorney Terry Levich Ross, the actor notes the date of separation is January 1, 2012. The couple was married in 2001.

Garth's lawyer, Melanie Mandles, simultaneously filed a response to the divorce petition ... in which she requests to have her name legally changed from Jennifer Facinelli back to Jennifer Garth.

Garth also checked the boxes for joint physical and legal custody of their children. According to the docs, both Peter and Jennie have agreed to pay for legal fees.

The couple announced the split earlier this month in a joint statement that said, "While we have decided to end our marriage, we both share the same deep love and devotion to our children."

Jennie recently admitted Peter's work on the "Twilight" movies put a strain on their relationship ... telling People.com, "He did everything he could to fly back every weekend ... [but] it took a real toll on our marriage."

Garth also said Facinelli asked her for a divorce last fall ... and it took her a while to "come to peace with it."