The former 'Real Housewives of New York' star -- who filed a lawsuit against AC back in February -- called out Cohen on Instagram Friday hours after the Princess of Wales' shocking cancer announcement.

In the statement, shared to her Instagram story, LM says Cohen enjoys being "cruel" to women, and adds Kate was no exception to the rule. She continues by saying Cohen needs to apologize to Catherine ... and finishes by calling on people in power to practice better leadership.

ICYMI ... Andy shared a tweet after TMZ obtained video of Prince William and Princess Catherine walking at a farm stand in Windsor, writing, "That ain't Kate..."

He also reportedly spoke about rumors of infidelity between William and on his podcast earlier this week ... all before Kate announced she's dealing with cancer.

All in all ... not a great look for Cohen -- who's just one of many celebs who have caught some flak for jokes and comments they made about KM before her video Friday.

Blake Lively has already apologized for cracking a joke about Middleton's photoshopped family pic while Kim Kardashian's stayed mum on her own post with a Princess Kate reference in the caption.

BTW ... McSweeney is suing Cohen and Bravo -- claiming they created a toxic work environment where her mental health and alcohol use disorder were exploited. So, she's got her own reasons for bringing attention to Cohen's statements.

That said, McSweeney's been telling people to lay off Kate for a while ... posting Sunday, March 17, wishing Middleton well while asking people to respect the princess' privacy and stop gossiping about her.