The cast of Merlin have dropped hints about what’s in store in the fifth series. Warning: Spoiler Alert!

In a recent interview with Digital Spy, Colin Morgan explained that his young wizard character is in a “ruthless mode” in the next series.

He said: "Merlin is becoming more ruthless, because he is becoming more solid in his beliefs. He's seeing things in a whole new way."

Speaking about Mordred (Alexander Vlahos) and Morgana’s (Katie McGrath) relationship, McGrath said: "You can't tell the story of Morgana without Mordred. They are interlinked, they are entwined, and from the very first episode [of series five], you see that."

Morgan added that the return of Mordred is "the biggest threat there's ever been" to Camelot and the reign of Arthur (Bradley James).

He said: "Anyone who knows the Arthurian legend knows what Mordred is destined to do... so that is the biggest threat, that is the biggest force."

Meanwhile, Merlin executive producer Julian Murphy hinted at the possibility of a sixth series of the BBC fantasy drama, saying: "There's conversations going on, but I can't really say any more than that."

Season five of Merlin will air on BBC One in the autumn.