[Khorum]

I'm pretty sure Loras will pop up right around Highgarden just when the Greyjoys and their Kraken banner come sailing upriver. Remember, aFfC ended on that note, with the Shield Islands falling to Theon's uncle, and greyjoy troops murdering and raping noblewomen in preparation to sailing up the mander, the first big city along the Mander happens to be highgarden.

Soon as Loras gets word of the Greyjoy invasion, I've no doubt he'd abandon his siege of Dragonstone keep and head home to protect his family's seat (and Margaery).

Now, I agree with a previous poster that Loras may exactly be a younger Jaime, complete with the sister-fucking part. It's entirely conceivable that he's been taking it up the ass too, but it's the same scenario with him and Jaime, his beloved sister gets shipped to King's Landing to marry, and in order to maintain a comfortable distance from her for illicit boinkings, he signs up for the kingsguard. Soon as he hears that she's in trouble, the facade is off, he either fakes his death or just plain runs off to save margaery and highgarden itself.

It's a pretty good setup too, the parallel becomes poignant when Jaime comes home to become Cersei's champion (although he's not terribly happy about it and he's pretty sure he's gotta get owned) and runs into a disguised Loras, who's there to rescue Margaery, they have similar motivations but are at different ends of their relationships with their respective manipulative sisters: Loras still young and in love, and Jaime jaded after learning what and who Cersei has been doing.