The 29-year-old was mentored by Cheryl, 31, during her time on the ITV talent show and was booted off in week eight.
Katie has never hidden the fact she blames judge Cheryl for her early exit, and she's not happy that the former Girls Aloud singer is still working on the show.
Discussing Cheryl's return to the panel this year, bitter Katie said: "I think she's just there for the money.
"People think that I have this huge grudge against Cheryl. And granted, I do. I'm p_ssed off for various reasons. If you ask me, she is fake as sh_t."
Twisting the knife in further, Katie told Star magazine that she doesn't think Cheryl is as nice as she's made out.
Katie continued: "I just think there's no substance to her. She can be very abrupt and rude. I don't think she's a very nice human.
"My advice to anyone who's going to be on the show would be to f*****g beg to get someone else as mentor."
Katie, who has struggled to secure a record deal since her appearance on the show, claims to be friends with new judge Rita Ora – and she apparently had a warning for her.
"I said Cheryl is a pr_ck, and Rita was like, Oh, sh_t really?' Because she asked what doing the show was like. I told her I hung out with Simon [Cowell] and Louis Walsh, and Cheryl sat with her Benson and Hedges in her dressing room staring at her diamonds. Rita, if you ever lose Cheryl, that's where she is!"
What do you think of Katie's comments? Let us know on Facebook and Twitter now.