Aegon is the son of Illyrio and Lemore

[Brad Stark]

Lemore is a mother, and not a Septa:

 

"Lemore was not near as innocent as she appeared. She had stretch marks on her belly that could only have come from childbirth"

 

"Lemore had changed out of her septa’s robes into garb more befitting the wife or daughter of a prosperous merchant. Tyrion watched her closely. He had sniffed out the truth beneath the dyed blue hair of Griff and Young Griff easily enough, and Yandry and Ysilla seemed to be no more than they claimed to be, whilst Duck was somewhat less. Lemore, though … Who is she, really? Why is she here? Not for gold, I’d judge. What is this prince to her? Was she ever a true septa? "

 

 

She has been with Griff a long time, working under Illyrio's orders:

 

“We have gone to great lengths to keep Prince Aegon hidden all these years,” Lemore reminded him. 

 

“Illyrio could not have been expected to know that the girl would choose to remain at Slaver’s Bay.” 

  “No more than he knew that the Beggar King would die young, or that Khal Drogo would follow him into the grave. Very little of what the fat man has anticipated has come to pass.” Griff slapped the hilt of his long-sword with a gloved hand. “I have danced to the fat man’s pipes for years, Lemore. What has it availed us? The prince is a man grown. His time is—” 

 

 

I suspect Lemore might be Serra, Illyrio second wife:

 

" Inside was a painted likeness of a woman with big blue eyes and pale golden hair streaked by silver"

 

"When the lad emerged from the cabin with Lemore by his side, Griff looked him over carefully from head to heel. The prince wore sword and dagger, black boots polished to a high sheen, a black cloak lined with blood-red silk. With his hair washed and cut and freshly dyed a deep, dark blue, his eyes looked blue as well. At his throat he wore three huge square-cut rubies on a chain of black iron, a gift from Magister Illyrio. Red and black. Dragon colors. That was good. “You look a proper prince,” he told the boy. "

 

 

We know the blood of Valeriya gives Targaryen traits in the free cities.

 

"“The blue hair makes your eyes seem blue, that’s good. And the tale of how you color it in honor of your dead Tyroshi mother was so touching it almost made me cry. Still, a curious man might wonder why some sellsword’s whelp would need a soiled septa to instruct him in the Faith"

 

 

What I suspect is Illyrio and Varys were originally scheming to put Daenerys on the throne.  Serra got pregnant, and their boy was born with Targaryen features.  As he grew and developed them more, they decided they could pass him off as Aegon Targaryen, put him on the throne instead, and made up the story about the pisswater prince.  Serra had to 'die of the plague' so she could assume the identity of Septa Lemore, and raise the boy.  They continued to back Daenerys, as she'd take the risk of invading and conquering of Westeros, only to have Aegon show up with a better claim to the throne if she won or after she lost.  They decided it was a good time to send 'Aegon' in now, as claims to the throne are weak, and Daenerys is nowhere to be found.

[Visenya Stark]

I guess Lemore could be Serra. This idea is slightly more probable than her being Ashara.

Illyrio and Varys couldn't have been planning to put Dany on the throne, otherwise, they would have taken care of her from the very beginning. They abandoned Dany & Viserys and looked after "Aegon".

[Ser Lepus]

What I suspect is Illyrio and Varys were originally scheming to put Daenerys on the throne.  Serra got pregnant, and their boy was born with Targaryen features.  As he grew and developed them more, they decided they could pass him off as Aegon Targaryen, put him on the throne instead, and made up the story about the pisswater prince.  Serra had to 'die of the plague' so she could assume the identity of Septa Lemore, and raise the boy.  They continued to back Daenerys, as she'd take the risk of invading and conquering of Westeros, only to have Aegon show up with a better claim to the throne if she won or after she lost.  They decided it was a good time to send 'Aegon' in now, as claims to the throne are weak, and Daenerys is nowhere to be found.

The main problem I see with that theory is that would require that Connington didn't realize the little boy he was raising was 3 years younger than he was told (and three years makes huge difference for a little kid). You could maybe argue that Connington doesn't know crap about children and can't notice the difference between a four years old and a seven years old, or between a seven years old and a ten years old, but it also requires that nobody else notices it.

[mediterraneo]

How do you know about the age of the son of Illyrio and Serra?

[Ser Lepus]

How do you know about the age of the son of Illyrio and Serra?

 

@Brad Stark's theory is that fAegon was born after Daenerys, and she is around 3 years younger that the true Aegon.

[Brad Stark]

The main problem I see with that theory is that would require that Connington didn't realize the little boy he was raising was 3 years younger than he was told (and three years makes huge difference for a little kid). You could maybe argue that Connington doesn't know crap about children and can't notice the difference between a four years old and a seven years old, or between a seven years old and a ten years old, but it also requires that nobody else notices it.

 

I believe Connington has to be in on the plot unless Griff really is Aegon,  "A true friend, our Lord Connington. He must be, to remain so fiercely loyal to the grandson of the king who took his lands and titles and sent him into exile."  His story is he was sent to exile as a ploy so he could raise Prince Aegon.  Far more likely, he was really exiled.

 

Thinking about it more, I'd bet Illyrio and Varys planned to help put Viserys on the throne originally.  But regardless, I believe this is a crime of opportunity, they changed whatever plan they had after they realized Illyrio had a son who could pass as Aegon.  This probably wasn't when Aegon was born, who most likely was bald and blue eyed, and grew up as any other kid until someone joked he looked like a Targaryen and Illyrio got the idea.  No way to put an age on when this happened.