Some of you might have seen the older blog post I wrote to promote "A Different Song," an A Song of Ice and Fire fan-fic depicting Ned Stark and the Northern cavalry interrupting the Sack of King's Landing. They discover Jaime Lannister has already killed Aerys the Mad King and together Ned and Jaime rescue Princess Elia Martell and her daughter Rhaenys from the vile Gregor Clegane and Amory Lorch respectively. It's a pretty entertaining story so far, but the author is rather slow in updating.
Well, the same alternate-history forum that spawned "A Different Song" spawned an unofficial sequel/spinoff, "The Lion of the North." The author would rather not post it on fanfiction.net, so you can read it on Space Battles or (without reader comments) An Archive of Our Own. And he certainly keeps the updates flowing. The gist of it is that King Robert Baratheon and Tywin Lannister connive to kill Elia and her children (I think in this continuity Aegon survived, which he didn't in "A Different Song"), leading to a permanent breach between the Lannisters father and son. After Jaime is too argumentative, Tywin disinherits him and prevails on Robert to expel him from the Kingsguard. He leaves for the North with Ned and things go from there...
Although I really don't like some of the stuff that goes on in King's Landing (it involves bringing in Melisandre a generation early and giving her magical powers that canon does not indicate she has, making the whole situation needlessly complicated), the stuff following Jaime, Ned, Catelyn, and even the young Tyrion is really well-done. The most recent update is even pretty funny--kids (in this case Robb and Jon) say the darnedst things upon meeting dwarfs.
So check it out!