Jennie Garth (L) and actor Peter Facinelli attend the 2010 Boys and Girls Clubs of America's Chairman's Gala at The Waldorf Astoria on June 2, 2010 in New York City. Credit: Gary Gershoff/

Although Jennie Garth and Peter Facinelli only officially confirmed their split to Us Weekly on March 13, the pair have actually been apart for some time.

"It's been over for months, maybe even a year," says one insider of the couple, who met in 1996 and wed in Santa Barbara in 2001. "They kept up some sort of charade for their kids." (Garth and Facinelli share daughters Luca, 14, Lola, 9, and Fiona, 5.)

Adds another friend, "They've been working on the marriage for awhile. It was not something they took lightly."

On Wednesday, Facinelli, 38, filed for divorce in L.A. County Superior Court. Citing "irreconcilable differences" as the cause of their breakup, the Twilight actor asked for joint physical and legal custody of their three kids. Both stars have agreed to pay legal fees.

In the meantime, Garth is staying strong as she promotes her upcoming CMT series, Jennie Garth: A Little Bit of Country.

"We're doing great," the 39-year-old told Access Hollywood hosts Billy Bush and Kit Hoover March 20.