According to reports, Mel B matched with Zac on an exclusive dating app for celebrities last year, and exchanged "flirty messages" before hooking up.
"He ended up driving over to her pad," a friend told The Sun. "They hit it off and spent a few enjoyable hours together."
The source adds that Mel and Zac both knew the hook up was just for fun, and it wouldn't turn into a relationship.
"It wasn't exactly a meeting of minds. Neither saw it as long-term, but there was chemistry. Mel thought Zac had an amazing body," they said.