Aemond Targaryen is the second son and third child of Kings Viserys and Queen Alicent. As a child, his brothers and nephew mock him because he doesn't have a dragon, inspiring him to claim Vhagar at Laena Velaryon's funeral.
Aemond has a lot of animosity toward his older brother, who he sees as cruel and unfit to be king. He even tells him in episode nine that he would be a better king, and Aegon doesn't disagree. He also never misses a chance to make fun of his nephews Jacaerys, Lucerys, and Joffrey over rumours they're bastards and really the sons of Ser Harwin Strong. Aemond does seem to have a close and protective relationship with his sister Helaena, however.