The finale of "Once Upon a Time" season 4 hinted that Merlin will be a key figure in saving Emma from the dark side, and it appears that the show is moving on to Camelot. According to a report from TVLine, the show's latest casting call reveals some of the key characters that will be introduced in season 5. 

According to the report, the casting directors are searching for a black British actor in his 30's to early 40's to portray Merlin. He must have a natural British accent to portray "a man with great wisdom and intelligence beyond his years." Merlin is also described as a man "who has always put duty in front of his own desires, even at great personal cost." 

The casting call is also hunting for a man in his 30's to 40's to play King Arthur and he must also command a strong British accent. Arthur is hinted to be a just ruler but deep inside is someone who carries a grudge to the grave, a master manipulator, and harbors eternal love for Guinevere which can sometimes be excessively controlling. 

For the role of Queen Guinevere, they are looking for a Latina actress in her mid-20's to early 30's and will portray a "headstrong queen." In Arthurian lore, Guinevere fell in love with Arthur's best knight, Sir Lancelot, who was also seen in "Once Upon a Time," played by Sinqua Walls. 

Lancelot died in the previous season but it is possible that his relationship with Guinevere may still have effects on her current relationship with Arthur.  

As pointed out by TVFanatic, "Once Upon a Time" is known for giving characters a dark twist. King Arthur is already filled with troubles for having a bastard son, Mordred, either through his sister or aunt depending on different versions of Arthurian lore. Merlin, a sorceror, may also have deep secrets such as the source of his powers. 

"Once Upon a Time" season 5 premieres this fall.