Brumand the Proud, Brumant, Brumart, Brumax
He was a nephew of King Claudas and one of his knights.
One Eastertime, the knights of Claudas’ court were discussing who was the best knight of the world. Everyone said it was Lancelot except Brumant, who said it was not Lancelot because Lancelot had never dared sit in the Siege Perilous. Although Claudas tried to dissuade him, Brumant swore to sit in the Siege Perilous on Whitsunday.
By the time Brumant arrived at Camelot, he was weeping (perhaps he had sobered up and realized what kind of vow he had sworn). He gave Lancelot a letter, telling him to read it in the event of Brumant’s death. Then, saying,
I shall die for doing what you never ventured to do.
Brumant sat in the Siege Perilous. A fire fell on him, from whence no one knew. It gave him just time to say,
By pride one gets but shame. I die by God's vengeance,
before it consumed him to ashes. An evil smell filled the hall, but passed quickly. All the knights moved away from the holocaust except Lancelot, who, refusing to move from his own chair beside the Siege Perilous, remained unharmed.
The letter Brumant had given Lancelot told the whole story of the rash vow. When Brumant’s three brothers, Canart, Cadant and Alibel, got the news from England, they took comfort in the thought that Brumant’s was an honorable death.
Source
Vulgate Lancelot | 1215-1230