Jennie Garth's feeling a deep sadness this week after fleeing the L.A. wildfires ... but, she thankful she's got people to fall back on -- including her ex-husband.

The "Beverly Hills, 90210" alum took to Instagram to give her fans an update on her family's safety after evacuating not once, but twice earlier this week ... forced out of their home by the massive Pacific Palisades wildfire on L.A.'s west side.

Garth says she and her family are fine ... but, her heart breaks for her city and everyone who lost their home in the fire.

While she and her daughters had to hastily evacuate, Jennie says their house somehow survived the flames ... and, she explains they're probably headed back.

Jennie heaps praise on her ex-husband Peter Facinelli ... who she says let her and their kiddos, her dogs and her husband David Abrams stay with him and his family.

Garth ends her message by shouting out the firefighters battling the blaze ... before cutting a mental health PSA into the final seconds of the clip.

Garth and Facinelli -- best known for playing Dr. Carlisle Cullen in the "Twilight" series -- married in 2001 after meeting on the set of "An Unfinished Affair" in 1995. During their 12-year marriage, Jennie and Peter had three daughters together. They divorced in 2013.

The Palisades Fire has burned nearly 20K acres. The Eaton Fire near Pasadena in northeastern L.A. has burned about 14K acres. Neither fire has been contained at this point.