According to rumours, the couple have been dating for the last 3 months but have apparently now decided to call it quits.
"They're no longer together. They were never serious, though; it was just a casual thing and it fizzled," the first source told US magazine.
"They were never in the same place at the same time."
To be honest, we never knew for sure whether Lily and Zac were actually dating or not, although according to reports, there were several sightings of the fledgling lovebirds holding hands in LA way back in February.
It doesn't sound like the break was much of a surprise to the second of these mysterious sources, who added: "Zac was never very serious about her. He didn't talk about her to friends."
"It's true that their schedules are crazy right now, which isn't conducive to a relationship being easy."
We're not sure what we think about all this, but what do you think? Did you see this coming or do you think they were just good friends all along?
Comments below please!