They "are in a serious relationship and in love," reads a US Weekly report. Cute!
"They spent the holidays together, with part of that time in Santa Barbara," the publication revealed.
In 2014, they were first romantically linked to one another, and it was reported that Zac was "really good to her".
"The relationship just wasn’t working out," said a source to Us Weekly. "She came back to L.A., and it never got going again."
They dated for less than one year, but are still amicable, with Sarah following Zac's Instagram still.
Well, Halston might not be the ex that fans wanted Zac to get back with, but we're so happy for them both.