The 45-year-old actress recently went public with her new man, who is 20 years her junior, and wasn't about to back down from an Instagram squabble with the 54-year-old "Joe Dirt" star after he mocked her penchant for younger men.
The feud began after Kate posted a video of herself cuddling a baby cheetah, taken during filming for her new TV series, "The Widow", in South Africa.
Spade cracked: "You like them young! (now dont fight back and roast me just quietly stew and take the hit) (sic)."
But Kate wasn't about to take the high road and shot back: "never going to happen grandpa."
The "Pearl Harbor" star and her toyboy lover, who broke off his summer engagement to Ariana Grande in October (2018), have been taking hits for weeks about their two-decade age difference, prompting Davidson to poke fun at the fallout during a sketch on his weekly comedy show "Saturday Night Live" earlier this month.
"Apparently people have a crazy fascination with our age difference," he said. "It doesn't really bother us, but then again I'm new to this.
"So if you have questions about a relationship with a big age difference, just ask Leonardo DiCaprio, Jason Statham, Michael Douglas, Richard Gere, Jeff Goldblum, Scott Disick, Dane Cook, Derek Jeter, Bruce Willis, Harrison Ford, Tommy Lee, Alec Baldwin, Sean Penn and whoever the president of France is."
All the stars he mentioned are dating women who are much younger.