"I'm not going to lie, I was not thrilled when I first heard about it," Nicky, 37, told Barrymore, 46. "I watch the show, I love the show. I think it's hysterical."
Despite being a fan of the series, Nicky still had her reservations about her mom's involvement.
"The drama, the fighting — it's a bit crazy," she continued. "But she has assured me that she does not curse and she does not fight. So, I said, 'Okay, have fun!'"
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"First of all, my mom was so shady about the whole thing," Nicky said on Paris' This Is Paris podcast. "Pretty much every year this rumor surfaces: 'Kathy Hilton is joining The Real Housewives of Beverly Hills.' And we're like, 'No she's not.' This year was no different."
When Nicky asked about the speculation, Kathy denied the rumors and said: "'Well, they've asked me and I'm thinking about it, but I'm probably not going to do it.'"
Once Nicky and Paris, 40, learned that the rumors were true, the famous sisters didn't talk to Kathy for "a few days."
"I'm not knocking the show, I love the show. I am a huge fan," Nicky said. "But if someone were to ask me, 'Do you want your mother on it?' No!"
PEOPLE confirmed last October that Kathy was cast on season 11 of RHOBH. She will join sister Kyle Richards, who has been a part of the franchise since it premiered in 2010. Their sister Kim Richards previously starred on the show for five seasons.
Before the casting news was made official, Kyle, 52, dished on whether Kathy would ever become an RHOBH star.
"I mean, I would be happy … I've had one sister on, why not have another sister on? My sister Kathy is actually — people don't know this, but she's one the funniest people there is," she said on Watch What Happens Live with Andy Cohen in 2019. "She's a practical joker and she's very, very funny. So I think she would be an amazing Housewife, actually."
The Real Housewives of Beverly Hills returns May 19 at 8 p.m. ET on Bravo.