Maggy the Frog

"When will I wed the prince?" Cersei asked.

"Never. You will wed the king."

"I will be queen, though?" asked the younger her.

"Aye." Malice gleamed in Maggys yellow eyes. "Queen you shall be . . . until there comes another, younger and more beautiful, to cast you down and take all that you hold dear."

"Will the king and I have children?" she asked.

"Oh, aye. Six-and-ten for him, and three for you."

The old woman was not done with her, however. "Gold shall be their crowns and gold their shrouds," she said. "And when your tears have drowned you, the valonqar shall wrap his hands about your pale white throat and choke the life from you."

This prophecy has, in part, already come true.

Cersei didn't marry the prince, but the king: in fact the marriage with Rhaegar was cancelled and Cersei married King Robert Baratheon, becoming his queen.

About the younger and more beautiful queen several suppositions were proposed. Most likely ones are: Dany Targaryen, Margaery Tyrell and Sansa Stark.

About the sons' number the prophecy shows how Cersei conceived her three sons not with the king (Robert), but with her brother Jaime. While Robert gave birth to even sixteen bastards, whose identities are until now unknow.

The phrase: “Gold shall be their crowns” seems to point out that all her three children will be kings or queens. Joffrey was king, and Tommen is at this very moment. About Myrcella it suggests that maybe she will be crowned as queen in Sunspear by Doran, inciting the Dornishmen to revolt. The words “ and gold their shrouds” make us to believe that all the three kings will die and Cersei will be still alive to see that.

As long as her little brother will come to choke her to death. The litlle brother could be Tyrion, who has always shown poor family affection to Cersei and has many reasons to see her dead. Jaime remains a suitable candidate too. In fact, he came out as second from his mother's womb, gripping Cersei's heel.

So, even if for this short delay, Cersei is the first-born son.