Stefanie Keenan/Getty Paris, Kathy and Nicky Hilton
On Paris' newly launched podcast, This Is Paris, the two opened up about learning that their mom had signed on to the Bravo show's upcoming season, saying they didn't find out until Kathy was already filming.
"First of all, my mom was so shady about the whole thing," said Nicky, 37. "Pretty much every year this rumors surfaces: 'Kathy Hilton is joining The Real Housewives of Beverly Hills.' And we're like, 'No she's not.' This year was no different."
But after the rumors began spreading faster than usual, Nicky said she asked her mom directly about the casting speculation — and Kathy denied the story.
"I asked her, 'Mom, are you going to be on the show?' She's like, 'No,'" she said, adding that it wasn't until later that her mom confessed that she'd been asked to join the cast.
"She goes, 'Well, they've asked me and I'm thinking about it, but I'm probably not going to do it,'" Nicky recalled. "Cut to Paris and I in Soho walking down the street and our friend FaceTimes us being like, 'I see your mom is on the Real Housewives...PEOPLE magazine just confirmed it.'"
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The sisters said they didn't speak to Kathy for "a few days" before finally confronting her.
"I'm not knocking the show, I love the show. I am a huge fan," said Nicky. "But if someone were to ask me, 'Do you want your mother on it?' No!"
Nicky said that despite Kathy's sister Kyle Richards appearing as a main cast member on RHOBH since 2010, their mother had never "seen the show" before signing on.
Michael Tran/FilmMagic Kim Richards, Kathy Hilton and Kyle Richards
"She doesn't know what she's getting into!" said Nicky. "Barron [Hilton] told me they were filming a few weeks from the house ... and he could hear the shouting from his bedroom."
In October, PEOPLE confirmed that Kathy will appear alongside Richards in the Bravo franchise's upcoming season 11. (Their other sister, Kim Richards, previously appeared on RHOBH for five seasons.)
And while both Nicky and Paris, 40, think their mom will make a great addition to the cast, they credit the COVID-19 pandemic with pushing her to join.
"My mom lied to us, pretended she wasn't doing it, wouldn't admit it," said Paris. "There's no way she would do this if there was not a pandemic happening and she wasn't so bored at home for the last year. There's no way she would have said yes. They've asked her every year."
"She's bored and she looks better than ever," Nicky added. "And I feel like she's like, 'Why not?'"
A premiere date for season 11 of RHOBH has not yet been announced.