Merlin: a new 13-part drama series on BBC One
Katie McGrath plays Morgana
As the adopted daughter of Uther Pendragon, she uses her power – and her looks – to good effect.
"She is Uther's ward. The first lady of Camelot and we are very aware that she is top dog. She is in control and she can manipulate all the men," explains Katie McGrath who plays the scheming beauty.
"She's very interesting, great fun to play. Not your average, retiring type of girl. She's a go-getter, stand up for herself kind of girl."
"There's a darker side to her. There are a lot of preconceived notions about Morgana. It becomes obvious that she is not an ordinary princess. She can do things that are not normal," she says.
"It's a completely different take on the legend. It borrows from all the legends. Because it's not based on actual fact it can be taken as it suits us and the audience."
Katie still has to pinch herself at having landed such a high profile role.
"Every now and again I'm standing in a corridor asking myself 'Is this real?' If you had told me that every day I get into this dress and watch sword fighting and dragons, I'd have thought you were mad," laughs the Dublin-born actress.
Her career credits to date include appearances in The Tudors, Eden and Damage on television and the upcoming horror movie Freakdog.
Katie has taken advantage of the huge experience within the cast, in particular by asking advice from Richard Wilson and Anthony Head.
"I'm quite new so having people like Richard and Anthony there who are so easy to talk to is great. It's daunting but everyone is so nice. Everyone is rooting for you. It's like a giant family," she smiles.
Despite her relative inexperience, Katie has a wise enough head on her shoulders to know that this is a moment in her career that she should savour.
If the show is a success, she would love to see Merlin, Arthur, Gwen and Morgana immortalised in toy figures, like the cast of Doctor Who.
"I want to have a little toy version of Morgana. I can then show it to my grandchildren one day," she says.
"So I can say I used to have a waist."