7. Change happens in Another's Sorrow, Season 5 Episode 4.
Merlin is not so easily persuaded that there is nothing wrong between Mithian and Hilda. When he can't stop thinking about it, he goes for a walk to help him sleep. Just as he's passing the guest wing, Mithian runs straight into him. Faced with a frantic princess, Merlin quickly leads her down a servants passage to get her to Gaius, keenly avoiding a newly awoken Hilda.