Now it seems the pair are definitely an item, after they were spied on a cosy Valentine's Day date in LA.
Just days after they were spotting holding hands at swanky Hollywood restaurant STK, the twosome were spied again, this time at trendy Soho House.
After indulging in a romantic treat, the pair snuck out of a back entrance and into a waiting car.
So could love be on the cards?
Last year, Lily was linked to her Abduction co-star Taylor Lautner, while Zac's high profile relationship with High School Musical co-star Vanessa Hudgens ended in 2010.
Hollywood's hottest new couple? Let us know in the comments box below...