Old Aemon did not answer Jon's question right away.
His fingers, clasped over his knees, tightened slightly, as though he were swiftly sorting through something in his mind.
When he heard the contents of the letter, his first thought was that Jon's unnamed mother had been a woman of House Targaryen.
Eddard Stark had fathered Jon with her. That was the most reasonable explanation.
Aegon had called Jon his "younger brother" not because they shared a father, but because Jon's mother was a Targaryen. By blood, that could make him a younger brother of sorts.
But he soon dismissed the thought.
Aerys had only one daughter, Daenerys, and when the Targaryen Dynasty fell, she had still been in Rhaella's womb.
Besides her, Rhaella and Aerys had no other legitimate daughters.
The timing did not fit.
As for a bastard daughter, he had never heard of Aerys having one.
Even if he had, Jon would only have been a bastard daughter's offspring.
Would Aegon Targaryen, the Dragonlord who sat upon the Iron Throne, have gone out of his way to write "younger brother" in a letter for a bastard daughter's offspring?
No.
That left only one other possibility.
Not his mother. His father.
What if Jon's father was not Eddard Stark, but a Targaryen?
What if Jon and Aegon shared the same father...
Old Aemon's fingers went still.
Rhaegar Targaryen.
Aegon claimed to be Rhaegar's son.
If Jon was also Rhaegar's son, then Aegon calling him his younger brother made sense.
Besides, given how much Eddard Stark valued honor, many people had found it hard to believe when he suddenly brought home a bastard son.
If that was the truth, it was entirely plausible.
But Rhaegar's wife had been Elia Martell, and they had only two legitimate children... Aegon and Rhaenys.