Viserys II/Theories
From A Wiki of Ice and Fire
Viserys II was the younger brother of Aegon III. As Aegon was most likely born around 120 AL Viserys was probably born short while after that.
Another clue is that Martin said that Viserys was in his fifties when he became king [1]. As he became king in 171 AL this places his birthyear at latest at 121 AL (and the birthyear of Aegon III at latest at 120).
