Have we had Star!Dunk yet?!
The stars are all gossiping biddies and they're always watching over the world seeing how things are going and bidding with each other over what's gonna be different when night comes again and they wake from their slumber to shine and to gossip... but sometimes they accidentally fall out of the sky. None of them know why it happens, it just does!
A fallen star actually started House Dayne. Dawn is made from captured starlight from that star, taken, willingly, in the moments of their death. It's been so long now, though, that no one remembers.
Stars have been falling for as long as the stars know. Some find ways to come back up to the night sky and others... well like the first Dayne, they stay among the humans, they live and they die there. Some find love and bring them back home with them, to the night sky, a new star forming in the night.
Dunk wasn't born in Flea Bottom. Rafe fell centuries ago, and he watched her live and he watched her die. When he falls, he doesn't mean to, it just happens. He's injured in the fall, and Ser Arlan finds him. Reluctantly sees him healed, because he looks young, he is young, as far as stars are concerned. When he's healed, he follows after Ser Arlan until the old man takes him on as his squire.
It doesn't occur to him that he should be trying to find ways to go back to the night sky. He's having too much fun being Ser Arlan's eternally young squire. Arlan on the other hand... Arlan remembers the falling star he'd seen that night he found the boy. He wonders, but he says nothing, he has no need of eternal youth and beauty. He's a hedge knight, what good are either of those things for him? So, he carries on, teaching the boy what he can. The boy's heart can stay right where it is, as far as Arlan's concerned. He has no need of it.
Arlan eventually dies before Ashford, like in canon, and Dunk goes off to the tourney. He still watches the shooting star with Egg, but he hopes it's not one of his siblings falling. Dunk's enjoying his time among the humans, but stars aren't meant to fall! They're not meant to stay here.
Everything else still happens, Aerion still attacks Tanselle and the puppeteers. Dunk still interferes. He's still accused of kidnapping Egg. He still asks for Trial by Combat and Aerion still demands Trial of Seven. Everything stays the same, until that moment, where Dunk's on his knees swearing to be Baelor's man, but Baelor...
It's still early enough in the day that some of the morning stars are still awake, not yet drifted off to slumber and they tell Dunk what they saw in the trial. The blow that will claim the prince's life.
Baelor is dying. Dunk realises it in the same moment Baelor's falling into his arms and no. No, he won't allow it. He won't. They say that to hold the heart of a star in your hand is to have eternal life, so Baelor can't die. He can't, because Dunk's heart is Baelor's. Dunk's life is Baelor's. All of him, it's Baelor's...
There is a blinding flash of light and when it passes, Baelor's young again, as young as he had been at Redrass. Hale. Whole. His eyes meet Dunk's and Dunk smiles, shining so brightly none can even stand to look upon them...
And when the time comes, after Baelor's lived a long life, and reigned through a golden age as king, he holds Dunk's hand and follows where Dunk leads, up into the night sky to live happily every after.