"Congrats to my beautiful friend," Garth wrote alongside a black-and-white pic of the pair. "#friends #bff #baby #iloveyou @torispelling."
Spelling and Garth were co-stars on Beverly Hills, 90210 from 1990 to 2000, and the pair have remained close friends ever since. They recently starred on the ABC Family show Mystery Girls in 2014, and their children are friends as well.
Spelling is mom to Liam, 9, Stella, 8, Hattie, 4, and Finn, 4 with McDermott, and Garth shares daughters Luca, 19, Lola, 13, and Fiona, 10 with ex-husband Peter Facinelli.
"[Jennie] brings out a side of me that I need and love. I don't laugh with anyone as much as I laugh with [her]," Spelling told Us Weekly in August 2014. "When we were young, we had times where we went out and went crazy, but … we had moments where we were home knitting in sweats. I remember being at your house at night, and we would go to Michaels and pick up food and hang out. We were DIYers then!"