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.
Q: Category: TOP OF THE POP CHARTS 
Clue: In 1978 he replaced his brothers at No. 1, who then replaced him; one of the brothers was a writer on all 3 songs
A: 
andy gibb