Joffrey became king when his father Robert Baratheon died in season 1.

Succeeding Joffrey cannot be Margaery,

Although she married Joffrey, their marriage was never consummated, so with his death the marriage becomes void. She is no longer the Queen, and reverts to being Margaery Tyrell.

Here's the Reddit discussion:

http://reddit.com/r/gameofthrones/comments/23cpoa/spoilers_s4e02just_answering_some_questions/

And the Imgur comments: http://imgur.com/gallery/nWbds

Will include Joffrey's succession order below.

These are Joffrey's two siblings, Myrcella and Tommen.

Remember that Joffrey, Tommen, and Myrcella are Baratheons first, not Lannisters first.

Myrcella is the middle child, and Tommen is the youngest.

Myrcella got shipped to Dorne by Tyrion in a betrothal to Trystane Martell, youngest son of Doran Martell, prince of Dorne (and Oberyn's older brother).

This is Tommen Baratheon.

He is Joffrey's heir because the laws of the Iron Throne say that males come before females in succession.

He looks different from the previous picture because a new actor is playing him in season 4 than played him in seasons 1 and 2. The show's producers wanted a more experienced actor for the part.

Myrcella Baratheon:

Myrcella comes after Tommen in the lines of succession.

Dorne has succession laws that say the next oldest sibling inherits regardless of gender.

Dorne's succession laws don't apply to the rest of Westeros, so Myrcella is Tommen's heir, not vice versa.

Cersei stays Queen Regent.

This means she effectively rules, because Tommen is not old enough to be king.

Regency ends and Tommen becomes king when he turns 16.

Tywin becomes The Hand.

So he effectively becomes in charge as everyone does what Tywin says, including Cersei.

Guess who comes after Myrcella? Robert's brother Stannis Baratheon.

Joffrey and his siblings derive their royalty from Robert Baratheon, and Stannis is his next oldest brother.

This is the entire reason behind Stannis' rebellion, because he believes himself to currently be the true heir since Joffrey, Myrcella, and Tommen are born of incest and have no Baratheon blood.

A summary of events that happened prior to season 1, episode 1 of Game of Thrones:

http://pandawhale.com/post/41050/game-of-thrones-prequel-infographic-from-oberyns-dialogue-with-tyrion-season-4-episode-1

Thanks for all the clarifying :)  So Stannis just needs to knock off those illegitimate kids!

Which has been his plan since season 1. We're only just now catching up to him.

But remember from that prequel infographic that Robert Baratheon himself usurped the throne.

From the Targaryens. And therefore Daenerys is the rightful heir.

Good point, maybe Stannis will get it, but only for a short time, Daenerys would be smart to let him fight the Lannisters first, less trouble for her later ;)

She's got dragons that, incidentally and incendiarially, can wipe out the White Walkers.

Forgot about that!  They might be begging her to take the throne ;)

The most plausible speculation of where they're going with all this is exactly what you described.

It doesn't get into what happens with Jon Snow, Arya, Sansa, Bran, and Tyrion, but it does pull together the main story lines nicely into an ending that restores what happened before Jaime Lannister and Robert Baratheon took the throne from the Targaryens.

"If you think this has a happy ending, you haven't been paying attention."

That line rings in my ears and in my head.

Ah, Ramsay Snow, the character everybody hates.

I souped up that page and even put the video on it:

http://pandawhale.com/post/30344/if-you-think-this-has-a-happy-ending-you-havent-been-paying-attention-ramsay-snow-to-theon-reek-greyjoy

Thank you!  You da best.

Happily! I've been a little Game of Thrones obsessed lately.

A Haiku re Incest

Kids born of incest

'Tis said, like flipping a coin.

(Or box of choc'lates.)

First ever incest haiku I've seen.

The weird thing is that everyone seems to know -- Ned Stark lost his head for it -- but no one except Stannis seems to want to do anything about it.

So, the *best* ever incest haiku you've seen.

Favorite Reddit line: Man, Margaery can't seem to get herself consumated, can she?

Best response to that: She should try not marrying gay men, or evil little shits with death wishes.

I also enjoyed this observation:

Note also that that's not why she isn't Queen. She was (briefly) Queen Consort, i.e. a Queen with no power or right to the throne. A Queen Consort derives any power from her influence with the King; A Queen Regnant rules in her own right (i.e. what Dany would be). A QueenRegent rules in her son's stead (what Cersei was, then wasn't, now is again). In the interim, Cersei was a Queen Dowager, that is, a bereaved Queen Consort. At this time she would also in English tradition have been called Queen Mother, as the mother of the ruling King. Traditionally a Queen Mother has zero power and in fact is expected to distance themselves from politics (ie. what Catelyn was expected to do, briefly). So the term isn't usually applied to Queen Regents.

Also, while the marriage was not consummated, it was blessed. In most medieval laws, as such it was legal but could be annulled. If the rules did have Mags inherit the throne, if it suited everyone, they could easily leave her be. Of course, the Damocles' Sword threat of it being annulled would hang over her head constantly, or more likely, would be immediately be plunged into her back by Cersei.

Now Margaery is a Queen Dowager; Cersei is a Queen Regent; Danaerys considers herself a Queen Regnant, and Selyse (i.e. Stannis' wife) considers herself Queen Consort. Ned Stark remains Queen of Heaven.

Now that image of Ned will be stuck in my brain!

Haha, me too Janill!

It's Littlefinger that had Joffrey killed!

He orchestrated it because chaos helps him.

Plus he gets to rescue Sansa, daughter of the woman he pines for, Cat.

I'm not sure why he wanted to frame Tyrion other than it takes heat off him and Sansa.

Maybe he didn't plan for Tyrion to be accused of the poisoning, no one knew Joffrey was going to make Tyrion cup bearer, so maybe that was just a little benefit? 

Littlefinger is cunning enough to want to make sure no one thought to blame him or Sansa.

Maybe Tyrion was just the easiest person to frame.

What is Littlefinger's reason for wanting Joffrey dead?  Does he stand to gain anything? 

Yes, because Littlefinger is not born to a royal family, the chaos from Joffrey's death is his way to climb up the social ladder; see season 3 on this page: http://gameofthrones.wikia.com/wiki/Petyr_Baelish

Littlefinger has always been in love with Sansa's mom too so getting Sansa out of there may have been his plan to get into Catelyn's good graces, before the red wedding took that away from him.

I'd expect him to want to avenge Catelyn's death both because he loved her and he wants more power.