The new couple follows in the footsteps of Once Upon A Time castmates Ginnifer Goodwin and Josh Dallas, who went public with their romance in April (12).
A source tells People.com, "(Morrison and Stan) met on set and are now exclusive. They started dating three months ago. They seem to be really happy together, but are trying to take things slow."
Morrison was previously engaged to her House co-star Jesse Spencer, while Stan dated Leighton Meester after they met on the set of Gossip Girl.