If the revealed card is Aegon Targaryen, you must put him into play if you can. You cannot put him into play if there is a copy in your dead pile, if a copy you own is in play under another player’s control, or if Barring the Gates is revealed. In that case he would simply remain on top of your deck. If he enters play as a duplicate, you cannot trigger his reaction.
If you put Aegon Targaryen into play with this effect, he is not an eligible choice for the card you place 1 gold on. You must choose a different character.