Merlin - Season 3 - Eps 6: The Changeling
Uther pressures Arthur into an arranged marriage with a visiting princess, Elena, though Merlin soon has reservations after discovering that Elena may not exactly be who she claims to be. As he tries to uncover the princess' dark secret, he learns that Elena's nanny is a Pixie. But what are their motivations? Who do they work for? And most important of all, what benefit do they get from her marriage to Arthur, the heir to the throne of Camelot? Will Merlin be able to get to the bottom of it all and prevent Arthur from making the biggest mistake of his life?
About Merlin

Title: Merlin
First Air Date: 2008-09-20
Last Air Date: 2012-12-24
Status: Ended
Rating: 7.8/10 (from 1001 votes)
Language: EN
Seasons: 5
Total Episodes: 65
Network: BBC One
Genres: Action & Adventure, Drama, Sci-Fi & Fantasy
Production Companies: Shine TV
Synopsis
The unlikely friendship between Merlin, a young man gifted with extraordinary magical powers, and Prince Arthur, heir to the crown of Camelot.
Cast

Colin Morgan
Merlin

Angel Coulby
Gwen

Bradley James
Arturo Pendragon

Katie McGrath
Morgana

Richard Wilson
Gaius

John Hurt
Kilgharrah (voice)

Tom Hopper
Percival

Rupert Young
Leon