Celebrity Big Brother contestant Katie, 40, commented on the stars as they walked down the red carpet, being just as scathing as usual.
Mocking Kelly, Katie posted a picture of a purple-haired troll and wrote: "Nice of Kelly O to make such an effort for Oscar night."
Not usually the type to hold back, Kelly blasted the social commentator. She wrote: "The perfect role for you would be Mr Cellophane in 'Chicago', as your jealousy is just that transparent. Aren't you bored of being mean? [sic]"
Unsurprisingly Katie wasn't phased by Kelly's reply. She quipped: "Bird you are supposed to be at the Oscars. Focus, love, focus."
Which seemed to really anger Kelly, who then lost her cool.
She wrote: "That's right - #CBB is over & no 1 gives a f*ck about u anymore. What a sad old woman u R that it takes me to make u relevant. [sic]"
This is not the first time Katie and Kelly have clashed. In January last year Kelly slammed Katie after she made comments about her mother Sharon.
She fumed: "U R a hypocritical human being that is addicted 2 attention U R so insignificant! Don't ever talk about my mother again! [sic]"
At the time, Sharon said in an open letter to her daughter: “My darling Kel, Katie Hopkins is a person with zero credibility. She has no respect for others and contributes nothing to society. Her comments and opinions of us are of no importance.”
What do you think Kelly's response to Katie?