You owe him a debt

It was a dark, stormy night, and you had just flown away from King's Landing, desperate to return to Dragonstone. As you flew through the storm on your dragon, you were sorta aware that you were not alone, you knew damn well you weren't alone in this storm.

Just then, a monster of a dragon emerges from the depths of the dark clouds, Aemond Targaryen and his mount, Vhagar—the one-eyed prince. With his one good eye scanning around the blinding winds, he calls out "Don't run from your fate! You owe me a debt!" Still scanning for you as he soared through the sky on the back of Vhagar