Shannen Doherty, Jennie Garth and Ian Ziering on April 19, 2012 in West Hollywood, California. Credit: Jeffrey Mayer/WireImage

Jennie Garth may not have a man in her life, but she'll always have her Beverly Hills, 90210 costars.

To celebrate her 40th birthday and the premiere of her CMT reality series A Little Bit Country, Garth hosted a party at The London in West Hollywood Thursday; Shannen Doherty, 41, and Ian Ziering, 48, showed up to rally around their newly single pal.

"Ian greeted Jennie and gave her a big kiss on the cheek," a partygoer tells Us Weekly. "They were all really sweet with each other and seem to be real friends. Jennie was definitely happy they were there to support her."

Garth's three daughters with ex Peter Facinelli -- Luca, 14, Lola, 9, and Fiona, 5 -- were also in attendance. "Jennie's eldest daughter stayed by her side for a while until Jennie went off to do interviews," the partygoer says. "While Jennie was doing interviews, her girls greeted incoming guests and posed for photos together."

It was an atypically joyous night for Garth, who's had to address her painful split from Facinelli ad nauseum while promoting her new show. "It's not something I'm dying to talk about, but it's something that's going on in my life. I'm not ashamed to talk about it," Garth said on The Ellen DeGeneres Show Friday. "I think by being open and honest with what I'm going through, maybe it helps somebody else."

She added: "At first, I wasn't sure how I was going to make it through, but I really learned that I am so much stronger than I thought I was."

When Facinelli, 38, filed for divorce on March 28, he asked for joint physical and legal custody of their daughters. "We're still so committed to being there for our girls," Garth explained of their decision to co-parent. "That's the most important thing for us."