"That one girl that got really famous wasn't nice at all," O'Day said. "Camila girl, she wasn't nice."
While participating in an Instagram Live Monday night, the "Marriage Boot Camp" star played a game of "F--k, Marry, Kill" with a few friends. O'Day, who is a member of the girl group Danity Kane, was asked to either "f--k," "marry" or "kill" three famous female bands -- Spice Girls, Fifth Harmony and Pussycat Dolls.
"Kill Pussycat Dolls," O'Day said. "Fifth Harmony... can I kill them too?"
"I like Fifth Harmony though," her friend said.
O'Day pointed out that a member of the now disbanded girl group was "really snotty" to her at an unnamed awards show. The "Making The Band" star added that Cabello in particular wasn't very friendly.
"And that one girl that got really famous wasn't nice at all," she added. "Camila girl, she wasn't nice."
Cabello, who left the girl group back in December 2016, has seen her hit "Havana" from her first solo album become Spotify's most-streamed song by a solo female artist in its history. The pop song won Video of the Year at the MTV Video Music Awards. Cabello took home a VMA for Artist of the Year, as well as four American Music Awards in October.
Fifth Harmony continued on without Cabello and recorded another album, but eventually the band broke up and announced an "indefinite hiatus" back in March. Like Cabello, Normani Kordei, Lauren Jauregui, Dinah Jane and Ally Brooke all went on to pursue solo careers.
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