Game of Thrones officially responded to the goof, too. In a statement, HBO tried to make light of the screw-up, saying, "The latte that appeared in the episode was a mistake. Daenerys had ordered an herbal tea." Welp. We'd hate to be the servant responsible for that mixup!
Interestingly, the company didn't confirm the cup was from Starbucks and vaguely described it as a "craft services coffee cup."
Prior to the statement from HBO, Bernie Caulfield, an executive producer on the show, acknowledged the cup's appearance in the scene was a mistake during an interview on WNYC's All of It with Alison Stewart.
"I can’t believe [it]” Caulfield said, per a recording of the interview (below). "Our on-set prop people and decorators are so, you know, so on it one thousand percent. I just honestly can’t, I’m like, is that really? Because nowadays you can’t believe what you see because people can put things into a photo that really doesn’t exist. But I guess maybe it was there. I’m not sure. But, yeah. We’re sorry! “
According to a report by Gothamist, she went on to joke about it. “Westeros was the first place to actually to have Starbucks," she said. "It’s a little known fact."