Interesting that Arthur would have to rescue the woman from the pire with his sword and not by from by his decree as King alone. Sounds like he and Merlin were on a mission.
Julian Murphy CultBox interview (Part 1) here:
-Series 5 will feature more Arthurian legends although they'll put a different spin on them.
-At least two of them can be found in this list (The Green Knight, Mark, King of Cornwall and Vivienne).
-Series 5 won't have as many meaty guest roles as the earlier series did due to the bigger amount of cast regulars.
-The Knights will be developed further.
-Series 5 will be darker.
-Guinevere is Queen so we'll see her in a wildly different role to before. They'll return to her family.
-There are some new female characters.
-They are going on very interesting journeys with both Morgana and Gwen, those two characters go on paths that people won't expect.
Janet Montgomery reveals some information about some of Princess Mithian's scenes: "so he gets stabbed with a sword and I hop over him escape the falling rubble and run to the wizard." Source.
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