She's been linked Sean 'Diddy' Combs, 48, since the early 2000s.
So when it came to the hip-hop star's guest list for his annual NYE bash, Cassie was a definite.
Prepping for Sunday's Miami shindig, the beauty hit the beach for some late December sun.
Diddy's darling! Cassie Ventura strips to her bikini as she hits the beach in Miami ahead of her man's NYE bash
Pre-gaming: Soaking up the rays in a revealing white bikini, Cassie, 31, looked happy and relaxed as she sips a drink
Party time: The skimpy swimsuit highlighted the beauty's shapely figure
Soaking up the rays in a revealing white bikini, Cassie, 31, looked happy and relaxed as she sipped a drink.
The skimpy swimsuit highlighted the beauty's shapely figure, as she posed with pals for pictures on the sand.
Later Cassie who was at Diddy's side as he welcomed 2018 on Sunday night, with an all-star bash.
The party - sponsored of course by Diddy's pricey Vodka Ciroc - was a fancy affair, with Instagram images showing sharp suits, fireworks and plenty of live performances.
Sun day: Prepping for the Miami shindig, the beauty soaked up that late December sun
Diddy's girl: The two have been linked for years, and are now going steady
Diddy Instagrammed throughout the night, despite telling fans he would be 'cutting his phone off'.
'FYI my phone is off! Going into 2018 stress Free. Happy New Year!!! Streaming live on REVOLT.TV'
The charismatic star obviously had a lackey on hand to post updates as he live streamed and postured with pals.
Party prep: Later Cassie who was at Diddy's side as he welcomed 2018
One image captioned 'Legacy Legacy Legacy!!!!' showed Diddy's three sons - his unofficial stepson Quincy, 26, and his biological sons Justin, 24, and Christian, 19.
Quincy is the son of Diddy's ex Kim Porter, with whom the star also had Christian and his ten-year-old twin daughters D’Lila and Jessie.
He is also the father of daughter Chance, ten, who is five months the twins senior and the daughter of Sarah Chapman, a long-term friend of Diddy's.
'Legacy Legacy Legacy!!' Diddy posted a shot of his three sons - unofficial stepson Quincy, 26, and his biological sons Justin, 24, and Christian, 19
GuestsL DJ Khaled brough his so Asahd to the star-studded bash
Meanwhile, Justin is the son of Diddy’s high school sweetheart Misa Hylton-Brim.
As for Cassie, the Me & U singer was first linked to Diddy shortly after she signed to his Bad Boy Records in the early 2000s.
The two are now going steady, but their relationship has gone through plenty of rough patches - including several break ups - over the years.
Living it up: The performances featured Diddy himself, who performed with his son and Khaled
Welcoming 2018 with a bang: Fireworks were set off to mark the new year
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