King Arthur's most famous son in legend is Mordred, his treacherous nephew (and sometimes son by his half-sister Morgause), who ultimately causes Arthur's downfall at the Battle of Camlann. While Mordred is the primary antagonist, earlier Welsh traditions mention other, less-known sons like Amr, whom Arthur himself killed, and Gwydre, but Mordred is central to the popular tales.
Kyduan is not Arthur's only child in Welsh Arthurian tradition – he is also said to have sons named Amr (Amhar), Gwydre, Llacheu and Duran.
The Alliterative Morte Arthure has Mordred grievously wound Arthur with the ceremonial sword Clarent, stolen for him from Arthur by his co-conspirator Guinevere, but then Arthur slashes off Mordred's sword arm and brutally skewers him up on the sword Caliburn (Excalibur).
The short answer is that his bastard son, Mordred, lead a coup de tat against Arthur's rule and Arthur was mortally wounded by Mordred at the resulting Battle of Camlann.
Arthur and Guinevere were childless. Arthur had an illegitimate child, Mordred, but never a legitimate one.
While Guinevere was locked in the Tower of London, King Arthur fought Mordred to regain his throne. Both King Arthur and Mordred died in their battle with each other. After King Arthur died, Guinevere joined a nunnery and stayed there until her death. She was buried next to King Arthur.
However, Mordred's faith in Arthur and Camelot was shattered after the imprisonment and death of his beloved Kara. Believing that Arthur had betrayed him and metaphorically spat on their friendship, Mordred turned against the king and joined Morgana once more.
Arthur's admiration continues to deepen as the story goes along. However, after discovering of Meliodas's betrayal, Arthur accepted the fact that Meliodas was the enemy. He stated that he would never forgive Meliodas for what he had done, and then tries to kill Meliodas.
Just to clarify for any readers in case there was any confusion, the three wives of Arthur in Welsh tradition were indeed named Guinevere (or rather, Gwenhwyfar), but the three mistresses had their own names.
In the Tavola Ritonda, Camelot is abandoned and falls to ruin after the death of Arthur.
Mordred has a similar issue where she hates being called a woman because it likely implies she's weak. Calling her male disregards who she is however.
Lancelot sacrificed himself in Arthur's place to banish the Dorocha, leaving Arthur deeply saddened. He held a memorial for Lancelot and made a speech naming him as the noblest knight he'd ever known (The Darkest Hour).
In some versions, Arthur and Morgause remain ignorant of their blood relationship and Mordred is raised by Morgause and her husband along with her other children. In Le Morte d'Arthur and some other stories, Arthur learns the truth about Mordred and, horrified, attempts to have him killed.
Merlin loves Arthur due to their intertwined destiny, where Merlin's magic exists to protect Arthur and guide him to become the great king he's fated to be, fostering a deep bond of friendship, loyalty, and profound care that evolves from obligation to genuine love, with some interpretations suggesting romantic love as well, especially given their willingness to sacrifice everything for each other.
Arthur met his daughter Guinevere, and fell instantly in love. Merlin tried to persuade Arthur against marrying her, telling him that she would lead to his and his country's ruin. Arthur loved her too much, and married her anyway.
Although Mary is said to have been more attractive than her sister, Anne seems to have been more ambitious and intelligent. When the King took an interest in Anne, she refused to become his mistress. By the middle of 1526, Henry was determined to marry her.
In the Arthurian legends, Nimue's most prominent role is that of the woman who magically imprisoned Merlin. According to Malory, Merlin fell in love with her, and in an effort to win her favor, began teaching her his magic.
The "Christianized" version it's because he was embattled with Morgan le Fay at the time. In the pagan version he was Fae and once he'd given Arthur the prophesy warning him that involvement with Guinevere would mean the ruin of his kingdom, was prohibited from interfering further by Fae law.
Zeldris「ゼルドリス」 is the current king of the Demon Clan, the lover of the Vampire, Gelda, the younger brother of Meliodas, the surrogate father to Percival and the youngest son of the previous Demon King.
Merlin's magic was so powerful he was able to achieve immortality as shown in The Diamond of the Day as he was capable of living forever as he was still alive even in modern times. His immortality may be because of his powerful magic or his destiny that ties him with the return of Arthur.
Left in charge, Mordred counterfieted letters telling of Arthur's death in battle. He then called a parliament to name him king, had himself crowned at Canterbury, and tried to marry Guenevere, but she tricked him and barricaded herself in the Tower of London.
In Geoffrey, Arthur passes his crown to his relative Constantine after being mortally wounded by the traitor Mordred in the Battle of Camlann. Geoffrey identifies Gildas' "royal youths" as Mordred's two sons, who, along with their Saxon allies, continue their father's insurrection after his death.
Mordred. Mordred was known to be Arthur's greatest enemy, sent to destroy him. His parents are Arthur's half-sister Morgause and Arthur himself.