According to the original novel, the singer who was tried by Joffrey was not Marillion, but an unnamed tavern singer. Marillion, who was present at the Crossroads Inn when Catelyn captured Tyrion and accompanied them to the Vale, makes an appearance in the next books, but never in King's Landing.
The trivia item below may give away important plot points.
One of the heads on spikes that Joffrey has placed on the battlements of the Red Keep was a model of former president George W. Bush. After an official apology from HBO the episode was pulled from all digital platforms, including HBO Go and iTunes, and all shipments of the DVD box set featuring the show creators David Benioff and D.B. Weiss' commentary that drew attention to the use of the head as a prop were halted. An updated version of the episode with the head digitally replaced was released online on June 25, 2012.