Stashed in: Twitter!, GRRM
More context in Game of Thrones season 4 episode 2:
What the Twitter abbreviations MT, PRT, and HT mean...
Sansa Stark met The Vale's Lord Bronze Yohn Royce's son Ser Waymar in S1E1. Lord Royce is father of the very first casualty in the series!
All the nods to Game of Thrones book readers from the show, updated and with proper tags, through season 4.
[Spoilers] A Song of Ice and Fire: The Dornish Master Plan Part 1 - YouTube