We're talking about Arthurian legend, which you must already have heard of, King Arthur, the knights of the round table, all that. You've also certainly heard of Lancelot, but just in case, I'll remind you that he was the pupil of Viviane, the Lady of the Lake, and the faithful and devoted lover of Guinevere, the wife of King Arthur, as well as one of the bravest and most talented knights of the whole Round Table. Morgan le Fay was in love with him, as well as many young girls, but that has nothing to do with this story, which takes place at the beginning of his career as a knight.
This story is that of Galahad, Lancelot's best friend. To begin with, he was an opponent of King Arthur, who invited Lancelot to join him because he admired his bravery. Lancelot became his very close friend and managed to make him make peace with Arthur. Galahad, who understood Lancelot's feelings for Guinevere, encouraged him to declare himself, and they became [unclear - accomplices or lovers, depending on who it means]. Later, they separated to go on different quests, and Lancelot came across the grave of Galahad who, according to the epitaph, had died for love of him. He tried to kill himself but was stopped by one of Viviane's servants.
For my part, I'm convinced that Galahad was in love with Lancelot. Of course, it was one of the traditions of the time to sleep in the same bed as your close friends, but in general the other person knew about it, and in general you slept too, you didn't spend the night watching him sleep... Of course, Galahad was in favour of the affair between Lancelot and Guinevere, but I think that's because he had understood that he had no chance anyway, and any person who is in love in an unselfish way would prefer to see the object of his love with the person they love, rather than see them depressed and alone. Besides, the fact that their separation was fatal for Galahad and not for Lancelot proves that their relationship wasn't balanced, and yet Lancelot was still very attached to Galahad and considered him his dearest friend.
Some who consider that a relationship of courtly love doesn't have to be exclusively between people of the opposite sex don't hesitate to defend the existence of a real homosexual relationship between Galahad and Lancelot, as well as between Guinevere and the lady of Malehaut.
So, I guess in this version they aren't father and son...