But an Olsen source tells PEOPLE the pair are "definitely hooking up"
Eyebrows were raised when the duo was spotted taking in an off-Broadway performance of Sleep No More on Friday in Manhattan, but a rep for Timberlake, 30, says, “Justin is not romantically involved with anyone.”
Although Timberlake may indeed be single, an Ashley source says she and the actor are more than just friends.
“I’m not sure if Ashley is serious with Justin or not – they aren’t dating but they have hooked up recently,” the source tells PEOPLE.
“Ashley is a relationship person, much more than [her sister, Mary-Kate], so we’ll see.”
• Reporting by LESLEY MESSER AND MICHELLE TAN