Must have read all the books or at least know of Daenerys's vision of Rhaegar Targaryen singing The Song of Ice and Fire to his wife Elia Martell and their two babies before fading away.
Tyrion POV
"I don't think you should be meeting with your aunt." Tyrion Lannister said to the blue haired boy walking beside him along the ship's galley.
"I am inclined to agree but that would show weakness. We are not weak." the boy of six and ten replied.
"We?" Tyrion asked.
"Rhaenys." the blue haired boy who called himself Aegon said. From the shadows stepped a beautiful woman with silver hair of the Targaryen line but all the beauty and olive skin of a dornish woman. She was dressed like a true Targaryen Queen with jewels and a crown on her silver hair.
"How did you ever afford to do this?" Tyrion asked.
"We conquered what was ours with fire and blood." Rhaenys Targaryen said with a cool smooth voice that reminded him of her Scheming Uncle Oberyn Martell.
"What have you conquered, Princess if that is what you are?" Tyrion asked.
"Old Valyria." Rhaenys replied.
"This ship does not work with the Second Sons. It is ours." Aegon said.
"Who's body was dumped at the feet of Robert Baratheon after the Sack of King's Landing?" Tyrion asked with curiosity.
"Some orphaned girl and boy. It was so shameful." Aegon said.
"But luckily they were beaten so bloody, no one could tell if they were Targaryen or not." Rhaenys added.
The boat docked and the two Targaryens emerged on the deck to a crowd of Old Valyrians cheering for the return of their King and Queen.
"Loving Big Brother! You've finally returned to me!' A girl of five and ten ran onto the ship to hug Aegon. Her hair was long and silver with a gold chain around the top of her head with excess weaved into a braid running down her back.
"Do you see, Tyrion Lannister, I am the Prince that was Promised and I will re conquer my seven kingdoms in Fire and Blood even with winter coming. People will come begging to live near the heat of my dragons."
"Your dragons? But your aunt-"
"Never owned those dragons. Their real names, after their great ancestors are, Balerion, the black one, Vhagar the green one, and Meraxes the cream one." Aegon explained. "Balerion is mine, Meraxes belongs to my clever and loving wife, Rhaenys and Vhagar belongs to my half daft little wife Visenya."
"Visenya? Rhaegar did not have a third child." Tyrion said befuddled.
"Will you never understand? I thought you were a clever man, Tyrion Lannister. If our good friend Varys could switch one of us, why not switch all of us? Our mother, Elia Martell was with child during the Sack of King's Landing. Why would you not think Aerys Targaryen would send her with his Queen, Rhaella." Aegon asked.
"The Mad King wanted to keep Elia Martell as a hostage to ensure Dorne's loyalty." Tyrion Lannister argued.
"Don't tell me men never lied. Especially our great grand father. He lied and help Varys more handy than Tywin Lannister because he knew, though he may be mad, we could fix everything." Rhaenys said wisely.
"We can fix everything because the Prince who was promised, is me." Aegon Targaryen VI said with a sly smirk with an arm around each of his two sisters.
So Oberyn, you died for nothing. Elia was not murdered by the Mountain. But- could this be?