You will be given a trivia clue, and the category it belongs to. You should answer with the best answer that belongs in the category and is described by the clue. For simplicity, answers should be in all lower cased letters.

Category: I GOT 3 As, MOM! 
Clue: In legend, this pure knight found the Holy Grail
galahad

Category: SIBLING REVELRY 
Clue: Dingane became King of the Zulus in 1828 after taking part in the murder of this king, his own brother
shaka

Category: YULETIDE FAVORITES 
Clue: This Brenda Lee perennial failed to chart in 1958 & 1959, but its re-release in 1960 reached No. 14

"rockin\' around the christmas tree"