- If your opponent did not have any power on their faction card for you to discard, you have not met the pre-then condition and thus cannot have a King character you control gain 1 power.
Knight. Smuggler. The Seven.
Reaction: After you win a challenge in which Ser Davos Seaworth is participating, discard 1 power from the losing opponent's faction card. Then, you may have a King character you control gain 1 power.