From Daenerys’s vision at the House of the Undying, in Qarth:

“Aegon,” he said to a woman nursing a newborn babe in a great wooden bed. “What better name for a king?”
“Will you make a song for him?” the woman asked.
“He has a song,” the man replied. “He is the prince that was promised, and his is the song of ice and fire.”

Daenerys IV, A Clash of Kings
George R.R. Martin

Rhaegar Targeryen with little Aegon and Elia Martell: "His is the Song of Ice and Fire"
Rhaegar Targeryen with little Aegon and Elia Martell: “His is the Song of Ice and Fire”
Rhaegar Targeryen playing the arp for little Aegon and Elia Martell
Rhaegar Targeryen playing the arp for little Aegon and Elia Martell

#RhaegarTargaryen #EliaMartell #AegonTargaryen #Daenerys #HouseOfTheUndying #asongoficendfire #aclashofkings #georgerrmartin

Rhaegar Targaryen, with little Aegon and Elia Martell – A Clash of Kings