Rebecca Mader, Robert Carlyle

Zelena's wicked plan may soon come to fruition on Once Upon a Time!

We know that Zelena (Rebecca Mader) has already stolen Charming's (Josh Dallas) courage, but the exclusive sneak peek of Sunday's episode  below reveals that she's also succeeded in stealing Regina's (Lana Parrilla) heart. Now, she'll set her sights on obtaining Rumple's (Robert Carlyle) brains.

But why? Find out what she's after below:

Once Upon a Time airs Sundays at 8/7c on ABC.