Michael Keaton mourns his Mister Mom costar Teri Garr, who died on October 29 at the age of 79.

“This is a day I feared and knew would come,” Keaton, 73, wrote on Instagram about Garr, who revealed in 2002 that she had been diagnosed with multiple sclerosis.

“Forget how great she was as an actress and comedian. She was a wonderful woman. Not only great to work with, but also great to be around. AND go back and check out her comedic work – Man, was she awesome!!

The pair played a couple in the classic 1983 comedy about Jack Butler, a married father from Michigan who struggles with household chores when he is fired and his wife Caroline (Garr) returns to work. The film, in which Keaton played his first leading role, also starred the late Martin Mull and Christopher Lloyd.

Talking to PEOPLE while promoting Beetlejuice Beetlejuice just weeks before Garr died, Keaton fondly remembered his time working with her.

“First of all, I’m going to talk about the fantastic, and I mean fantastic legend, Teri Garr, how fantastic she is, and how sweet she is, and how much fun we had on this movie,” he said.

“Regardless of this movie, if you’re watching… Just go watch it Young Frankensteinman. And she’s still so amazing,” he added.

Keaton said he knew the script, written by John Hughes, would be a fantastic comedy.

“I remember reading the script. And I remember laughing out loud three or four times,” he said. “And to most people that seems like, ‘Well, that’s not much.’ But ask someone. Because the others you smile at, or you laugh, read and think about it a little, or you imagine it. But if something makes you laugh out loud, that’s encouraging, to say the least.”

Keaton was right. Thanks to the chemistry and banter between the two leads, the film received generally positive reviews. It earned $63 million at the box office (about $200 million in today’s dollars), making it one of the top 10 hits of the year.

Prior to Mister MomGarr made a name for himself in comedy, starring in hits like 1974 Young Frankenstein and 1982 Toetsiefor which she earned an Oscar nomination for Best Supporting Actress.

Garr died Tuesday “surrounded by family and friends,” publicist Heidi Schaeffer told PEOPLE.