Thorne shared a photo of her laying on top of the shirtless 25-year-old actor on a pool float wearing the same outfit she had (which was featured on her Snapchat) worn earlier on Sunday.
“Happy birthday Gregg!!!! I love you,” she captioned the image. “Always been such a wonderful person:) glad we are here through thick and thin. Let’s party you old man!!”
The actress also shared a video of balloons that spelled out “Happy Birthday G-Eazy” on her Snapchat on Sunday.
Thorne and Sulkin announced their split exclusively through PEOPLE in August, vowing to “always love each other.”
The actress, who came out as bisexual soon after the breakup, continued to work with her ex on the TV movie Drink, Slay, Love, where Sulkin tackled the leading man role while Thorne served as co-executive producer on.
“So happy to be executive producing this film and getting to work with the team again!! Watching dailies as we speak!!! @cierraramirez and @greggsulkin are killing it as leads!!” Thorne wrote on Instagram announcing the news.
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After jetting out of Los Angeles together, Disick and Thorne were spotted getting close and cuddly on Wednesday as they lounged on sun beds at a luxury private villa in the French Riviera. Thorne opted for an animal print bikini top and pale pink bottoms for the sunbathing session, and the two were also joined by the actress’ sister Dani, 24.
Of the PDA pics, one source tells PEOPLE that Thorne “really likes the attention” that comes with the new fling.