Anyone know what he whispered at the end?
He was whispering a fragmented version of the "prophecy" of the Night King and the Walkers that he told to the princess in Episode 1.
My guess is the point is it will convince Queen Alicent that one of her sons is fated to be the "King or a Queen" that is Targaryean, thus kicking off what is an inevitable civil war for the throne.
The bastard children of the Princess and her affair with Strong means that there is no blood ties to the Velaryon House. (Daemon's two daughters mean nothing since they are step children) If one side of the civil war had the allegiance of the Velaryon house, then that would likely stop any war, it would mean fighting would be pointless as one side would have a disproportional force in arms, men, money, influence, ships, etc, etc . But if Visery's sister just opts out, which she has indicated she will do, then she will just stay out of it. She has no desire for ambition nor the throne.
The knotty problem there is the true "heir" Laenor, is still alive somewhere. And if he's proven alive, that makes the Princess's children expendable. That might be enough to get "Auntie" to finally get off the sideline and start killing people.
What's going to be interesting is one eyed arrogant Aemond and his dragon against his "uncle" Daemon. You can see Daemon is amused by his "nephew", even impressed at his boldness. But also the kid is a complete psychopath.
I'd said it before, I'll say it again, the lesson here is always the same - Kill your enemies as fast as you can, be decisive and leave no doubt. Vaemond Valaryon lost his head for what? He spoke out and made idle threats when he should have killed his sister in law, taken control of the Velaryon family by force, then killed everyone in that throne room.
It's unfortunate that the GOT last few season fell apart. Because the Roose Bolton and Ramsey Snow/Bolton situation was really interesting. Roose knew his bastard "son" was a psychopath. However there was a cold efficiency in having all your problems killed outright. Roose wanted the net effect of the total carnage, but not the reputation.
Love motivates sometimes. Fear motivates all the time.