Question: is aemon targaryen the mad king's brother?
Answer: He is the third son of King Maekar I Targaryen, and the older brother of King Aegon V Targaryen ("Egg" from the Dunk and Egg short stories by George R.R. Martin), the uncle of King Jaehaerys II Targaryen and thus the great-uncle of the Mad King and the great-great-uncle of Daenerys Targaryen.