I've seen a lot of speculation about Maggy's prophecy stated as fact recently, even though those interpretations aren't at all conclusive. Here, I'm going through the final part in some detail.
"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."
The first paragraph is crystal clear, it speaks of their respective bastards. The only thing worth pointing out is that only five of Robert's bastards are named, most are unaccounted for.
Cersei: Joffrey(dead), Myrcella, Tommen
Robert: Mya Stone, Bella, Edric Storm, Gendry, Barra(dead) + 11 unnamed
"Gold shall be their crowns..." = they will all rule as monarchs
Joffrey and Tommen already have fulfilled this, while Myrcella has not. There are basically three plausible ways for this to come about:
- Tommen dies and she inherits the Iron Throne.
- Doran and Arianne dies and she becomes Queen of Dorne as Trystane's wife, to whom she is betrothed.
- She marries a King, thus becoming Queen by marriage. It's unclear who that would be though.
The first implicitly means that her bastardry remains a secret, or she cannot inherit anything. It's admittedly within Tommen's power to legitimize her as a heir, so even this wouldn't completely rule it out. He's very unlikely to do that though, as it would badly undermine is own legitimacy too.
The Dornish more than suspect the truth about Cersei's children, yet they have made no move to break up the marriage contract. Arianne is fiery enough that she may well find an early grave, making Trystane the heir apparent moderately soon.
"... and gold shall be their shrouds"
has two common meanings in English, both of which are reasonably applicably here. It can either be a funeral cloth or a protecting deception. The latter being, of course, the claim that Robert is their biological father.
If the first meaning is true, the prophecy is about their deaths. It does, however, not in itself imply when
death will occur - which makes it rather a trivial statement in itself.
If the second meaning is true, the "golden" part can only mean Cersei - more than once spoken of as "golden twins" or "golden woman". Her lies about their parentage keeps them safe and in positions of power- as long as it holds.
"And when your tears have drowned you,..."
This clearly does not mean drowning in a literal sense, but to mourn gravely - possibly the loss of everything she considers important in her life. This is strongly implied by the first part of Maggy's prophecy
Queen you shall be, until there comes another, younger and more beautiful, to cast you down and take all that you hold dear.
The only things Cersei can realistically be claimed to love are, in alphabetical order, her children, Jaime and power. She has already, at least temporarily, lost both her power and Jaime. As this post is about her children, I'll focus on that part of it.
The two ways for her to lose her children are either their death, or what she considers utter and complete betrayal on their behalf, "You are no child of mine!". She did not stop loving Myrcella just because she was shipped away to Dorne. Both Tommen and Myrcella are storywise in solid positions for such betrayals as the Lannisters are facing ever-mounting tensions with both Tyrell and Martell. Should it transcend into outright hostilities, they will be forced to choose between their mother and their spouses.
Doran Martell and the Sand Snakes are already moving to infiltrate King's Landing to prepare for open rebellion. They may do this either independently or by joining forces with Aegon, whichever ends up being more suitable. As Myrcella seems quite fond of Trystane, it's definitely not a foregone conclusion what side she will side with. If Darkstar is brought to justice for his attack on her, that may tip it in favour of House Martell. Whether or not she survives it this will still fulfill the prophecy.
For Tommen, the situation is rather similiar. Margaery is in for a trial of uncertain outcome, if she gets convicted there will likely be no way to repair an alliance between Tyrell and Lannister. Tommen is very fond of both Cersei and Margaery, but if he founds out his mothers part in Margaery's undoing even mild-as-milkwater Tommen may abandon her.
So, the prophecy doesn't actually say that they will die young - that is the "speculation taken as fact" I mentioned in the beginning. There isn't really any evidence at all in favour of it beside this prophecy - which isn't exactly clear on the point.
shall wrap his hands about your pale white throat and choke the life from you."
To point out the obvious, this means Cersei will die a violent death. The intriguing point is the identity of the valonqar. The paragraph can be read in three different ways:
- Cersei's own younger brother, which means Tyrion or Jaime
- The younger brother in the context of her children, meaning Tommen
- Any younger brother at all
Tyrion in particular have good reasons to want her dead, is already a kinslayer and has pronounced a wish to kill her in person. Jaime is losing his infatuation with her and starts to see her for what she is. His redemption arc may well include killing her.
I have already pointed out a situation is which Tommen may turn on her, though he does not strike me as a potential murderer. The wording of the prophecy strongly suggests it however, it reads "the valonqar" and not "your valonqar" - the context is clearly that of her children as both Cersei's question and Maggy's former answers were about them.
Option 3 feels a bit far-fetched, that includes the greater part of all Westerosi males...
It can be noted that it's not mutually exclusive for Tommen to be the valonqar or die young as the choking described matches closely to Ser Waymar Royce's death in the Game of Thrones prologue, though Tommen-wight is probably crackpot territory.
It has been suggested that "valonqar" is gender-neutral and could thus also mean "younger sister". This all stems for Maester Aemon's musing about the word for "dragon" in the same language being neither masculine nor feminine. This feels like grasping for straws though, words for close relatives are almost invariably gender-specific in real-world languages while those for beasts need not be. We have actually not even seen any indications that the dragons themselves have a well-defined gender.