WARNING: The following contains major spoilers for Wizards: Tales of Arcadia, now available on Netflix.
When Tales of Arcadia teased an ancient warrior that would put the Trollhunters on a path towards doom, few knew exactly what this Green Knight would have in store and just how much a weapon of mass destruction he would be. As Wizards: Tales of Arcadia unravels, viewers discover he isn't operating on his own; he's actually a pawn of the Arcane Ones, who are looking to magically remake the world.
When the truth about the Knight's identity is revealed, it shakes the foundation of everything Douxie, Claire and the other heroes believe in as it's someone tied closely to Merlin, Camelot and the Master Wizard's quest to protect Earth. It is none other than King Arthur.
The Death of the King
The Green Knight is initially seen attacking the flying Camelot castle, which is what gets Douxie, Jim, Claire and Archie thrown through time and back to the 12th century. There they witness the battle at Killahead Bridge where Arthur's forces battle the Gumm-Gumm army led by Gunmar, but prior to this, they discover Arthur and Morgana's feud in the courtyard and how he didn't want his sister wielding magic and sympathizing with the enemy. He believed in Merlin, but he hated Morgana as he blamed her for Gwen's death.
Arthur grew bitter towards his sister, and this is why he wanted to imprison all magical beings, such as trolls, causing a rift to grow between him and Morgana. Eventually, he kills Morgana when she tries to interfere in his campaign of hate, but she's resurrected by the Arcane Ones as the ultimate sorceresses. In a union with Gunmar's forces, they destroy most of Camelot before taking apart most of Arthur's army at Killahead bridge.
Here, the king dies at the hand of the Arcane Ones, but as trolls and humans reunite, the tide is turned in Camelot's favor, allowing them to win the war. However, when Morgana is brought back from the Shadow Realm that Douxie trapped her in during this brawl, she begins to reclaim her humanity as she discovers Arthur's body has been repurposed.
The Green Knight Rises
No longer angry and at peace after centuries in the Shadow Realm, her outlook is different, and her heart breaks when she sees what befell the fallen king. The Arcane Ones stole his body and implanted dark magic in it, making him a mindless drone. He even wields a corrupted Excalibur, which is why Morgana can't get to his soul in the Shadow Realm. All his humanity has been wiped clean, and this encourages her to turn on the Arcane Ones as they seek Nari and the Genesis Seals to complete their purge of mankind. Morgana finally understands that they played her from the start and have been using her and Arthur as a means to an end where not even magical beings are safe.
Arthur blindly abides by their rule as he believes that after losing Gwen and killing his sister that humans aren't meant to rule. He's disappointed with himself and given up hope on his people, ergo why he wants to rebuild with the Arcane Ones. The Green Knight thinks this warped genocide will rebuild Earth, but he can't see the perverse scheme unfolding as he's trapped in the darkness, driven by pain after a life of loss.
His journey is compounded when he stabs Merlin to death in front Douxie, making it clear he is willing to sacrifice anyone to get the job done, even Morgana. This leads to them confronting each other in Arcadia, fighting to the death as Morgana has accepted that she may need to die in order to kill the Green Knight, as Arthur no longer exists.
DreamWorks' Wizards: Tales of Arcadia stars Colin O'Donoghue as Douxie, Emile Hirsch as Jim, Lexi Medrano as Claire, Charlie Saxton as Toby, Steven Yeun as Steve, David Bradley as Merlin, Lena Headey as Morgana, Diego Luna as Krel and Kelsey Grammer as Blinky. It is available now on Netflix.