game of thrones - Who is "the valonqar" from Cersei's prophecy?

Inspired by How many people of Arya's list are still alive?, and also the recent excerpt from The Winds of Winter.

In the prophecy of Maggy the Frog, Cersei is told quite a few true things, such as the number of children she will have, that Robert would have, that she would not marry Rhaegar, but Robert, that Melara Heatherspoon would die and

that Cersei would kill her -- threw her down a well.

She is also told that "the valonqar" will kill her:

And when your tears have drowned you, the valonqar shall wrap his hands about your pale white throat and choke the life from you.

(As a side note, this sounds like she will be killed by a wight)

Cersei seems to think that this valonqar is Tyrion. Mostly, I guess, because "valonqar" means "little brother", plus the fact that she does not like him very much. But since this is ASOIAF and GRRM, anything is possible, and it is not a given thing that Tyrion is this "valonqar". Since GRRM has opened the door for gender ambiguity in the prophecies, this might also apply to this "valonqar", which would make it "little sibling" instead.

A few possible suspects are: Tyrion, Jaime, Arya (or any of the Stark children), Loras Tyrell, Aegon, etc.

My personal opinion is that the queen mentioned in the prophecy is Daenerys, but that it is not her that is the killer.

Maggy: Aye. Queen you shall be... until there comes another, younger and more beautiful, to cast you down and take all that you hold dear

This is a major point in the books. Much of the plot depends on it. It is Cersei's motivation for the cold marriage to Robert and subsequently her murdering him. It is her reason for trying to kill Tyrion and for disliking him.

So, without using too much tinfoil, who is this valonqar that will finally do the deed we've been waiting five books and soon 20 years for?

I am looking for solid theories with support in the books. Such as the prophecy of Mirri Maaz Duur, which according to some has come to pass. (Though of course Cersei has not been killed yet).

I know some people will be itching to close this question as being too speculative or a list question or whatnot, but fact is, in ASOIAF these things are foreshadowed and hinted at by GRRM to such an extent that it goes beyond speculation. Also, this will be a hot topic when season 4 starts in a few days.

For example, with regard to Tyrion, we know he is motivated to kill Cersei, we know he has expressed the desire to do so, we know he has killed before, he even strangled Shae. The only obstacles now would be distance and power balance.