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While reading the White Book of the Kingsguard, Joffrey mentions Ser Duncan the Tall, the main character of the "Dunk and Egg" trilogy by George R.R. Martin. It is the second time Duncan is mentioned in the show, following Lord Snow (2011). Ser Arthur Dayne is mentioned for the first time, a legendary Kingsguard member (and the one who knighted Jaime) whose part in Robert's Rebellion is addressed in the sixth season.
Diana Rigg's surprised exclamation towards Gwendoline Christie's height, when the latter approached her table, was quite genuine. Rigg was aware that Gwendolyn was taller than most women, but was unprepared for just how tall. The producers kept it since it fit in so well with her character.
Although Valyrian steel and the Valyrian language are frequently mentioned on the show, the Valyrian civilization, its location and fate are hardly ever discussed in detail. Valyria was a grand capital of the Valyrian Freehold, which covered most of the continent of Essos. Four hundred years before the start of the show, the city was almost completely destroyed during the Doom of Valyria, a series of massive volcanic eruptions and earthquakes. The disaster also seriously reduced the dragon population on the continent, and the ensuing collapse of the Valyrian realm indirectly caused the surviving Targaryen family (and their dragons) to invade Westeros almost a century later. This episode is the second to explicitly mention the Doom (after a brief reference in A Man Without Honor (2012)), and the first to acknowledge the fact that the craft of manufacturing Valyrian steel was lost during the cataclysm (although a few blacksmiths can reforge existing Valyrian steel). The Doom of Valyria is actually the very first thing seen in the show's opening credits, depicted on one of the rotating rings as a city in flames on the slopes of an erupting volcano, next to a dragon.
The HBO subscriber streaming service HBO GO crashed minutes after this episode went live due to high usage.
The ratings for this episode are the highest in HBO's history since the series finale of The Sopranos (1999).