The 'Spring Breakers' actress ended her one-year relationship with her former flame at the end of 2012, but the pair have sparked speculation they have rekindled their romance after they were spotted canoodling at Ashley's 24th birthday party.
The 24-year-old star held a joint celebratory bash with her model friend Esther Houston last Friday - two days after her real birthday - at the Boom Boom Room in New York City.
A source said: "Ryan and Ashley were kissing each other all night."
The blonde beauty was rumoured to be dating James Franco after they seemed to be getting close on the set of 'Spring Breakers' last year, but the pair shot down those reports in October.
However, Ashley said earlier this year that she wasn't keen on getting into a new relationship because she hates the added pressure that comes with it, but she's not opposed to falling in love.
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She said previously: "If it happens, it happens. I'm 23 -- I could have a boyfriend tomorrow. But relationships are scary, because once you're in one, you have to face the idea of breaking up or staying together forever. It's scary."