Kate Beckinsale finally spilled the beans on what caused her weeks-long hospital stay -- after some harsh trolling about her appearance forced her to set the record straight.
The actress clapped back to one critic who commented her "ass ran away" under an IG vid of her in a revealing pink outfit ... saying the grief over her mom's stage 4 diagnosis and her stepdad's passing was so intense it burned a hole in her esophagus.
The actress explained she was vomiting copious amounts of blood over the diagnosis and found eating very challenging -- which led to her six-week hospitalization in March.
Among other things, shooting a movie centered on the theme of her character's father's death right after losing her stepfather, director Roy Battersby, IRL was triggering for Kate ... adding to her health woes. So, needless to say, she wasn't really concerned about what that critic thought about her ass.
Kate fierily concluded ... "Maybe you should worry about your own f***ing ass. I suggest shoving something up it -- like a large pineapple or a brick."
You'll recall, Kate posted concerning IGs of herself at the time ... looking frail with downtrodden facial expressions in the hospital -- but she kept the exact diagnosis under wraps until now.
Kate's made it consistently clear she doesn't back down from haters -- and recently she came for all those insisting she's had loads of work done over the years, branding them bullies.