King Arthur's elder sister, Morgan le Fay, used underhanded means to get pregnant with Arthur's child.
Meanwhile, Lancelot, who had just become a Knight of the Round Table and was serving as an envoy to a small kingdom, found himself in the same predicament as his king.
The princess of that kingdom, named Elaine, had been rescued by Lancelot during a war several years earlier. Ever since, she had been madly infatuated with him.
She had tried to make her feelings known, but Lancelot, who loved Arthur (Artoria) deeply, had rejected her without hesitation.
Princess Elaine was utterly heartbroken and had even tried to take her own life.
But her father talked her out of it.
The king established diplomatic relations with Arthur and asked King Arthur to appoint Lancelot as the channel for diplomacy between their kingdoms.
After all, by then Lancelot had made a name for himself on the battlefield and was at the height of his fame. His formidable skill, handsome face, and noble status made him the most sought-after match among the noblewomen of Britain and the surrounding kingdoms. The king also wanted a son-in-law like him.
It was a small matter, and Arthur knew nothing of the circumstances, so she readily agreed.
Princess Elaine was a good match in every way. She was pretty and gentle with others; it was only when it came to love that she could be unscrupulous.
During this routine diplomatic visit, Lancelot was given a sedative strong enough to knock out a bear by Princess Elaine and her father, who had spotted their chance.
Then, while Lancelot was unconscious, she forced him to sleep with her.
By the time Lancelot regained consciousness, two days had passed.
Furious when he learned what had happened, Lancelot drew Arondight, intent on killing Elaine