Aithusa airs at 8.15pm on Saturday 22nd October on BBC One and sees the mysterious Julius Borden arrive in Camelot with news of a magical secret that threatens to change the landscape of the kingdom for ever.

> Order the Series 4 Volume 1 DVD on Amazon.

In this clip, Gaius is disturbed by a pounding on the door. Much to his surprise the mysterious visitor is Borden, a man with whom he has a checkered history….

Are you looking forward to the episode? Let us know below…