The Strictly Come Dancing star split from Zane last month and appeared at the BAFTAs without her engagement ring.
However, last week the pair were spotted embracing at a West London hotel, sparking rumours that they were back together.
Brook has now confirmed her reunion with the Titanic actor, claiming she missed him too much to make the split permanent.
She told The Mirror: "We're so happy. It's just the best feeling being with him. I really missed Billy. We realised we're at our happiest when we are together.
"We needed to get away just to have some quality time together away from England. And to have a laugh - that's important isn't it?"
The couple attended a party at the Hotel Du Cap in Cannes on the weekend.