The 19-year-old actress sent her "love" to Sulkin on Instagram following her short-lived fling with reality star Scott Disick.
"Happy birthday Gregg!!!! I love you :)) always been such a wonderful person:) glad we are here through thick and thin. Let's party you old man!!" she captioned a picture of herself on Sulkin's back.
"After much thought and soul-searching, we have made the difficult decision to end our relationship," the stars said Aug. 15. "We will always love each other and have a deep respect for one another, as we have each grown to be better people because of our time together."
Thorne was linked to Disick this month after a date in Los Angeles, and flew to Cannes with the reality star last week. The pair were spotted kissing May 24, but Disick got close to his ex-girlfriend Chloe Bartoli the next day.
"I'm not talking to Scott or anyone else," Thorne tweeted after Disick was seen kissing Bartoli.