(CNN) -- British actors David Bradley and Mark Gatiss arrived at the party of film "The World's End" together last night at Comic-Con to discuss their upcoming BBC film "An Adventure In Space and Time."
But the pair also have another project in common now.
Bradley, who plays Walder Frey on "Game of Thrones," can now cite Gatiss as one of his fellow cast members on the show. Gatiss was recently announced to be joining the hit HBO series, but his role remains something of a surprise.
"I'm not allowed to tell you," Gatiss said. "I've done my filming. I'm glad I didn't tell anyone before this since it's a big secret. The announcement of (my casting) was obviously timed for Comic-Con and I'm rather overwhelmed with the reaction, honestly. It's a great show with so many brilliant people in it."
Gatiss' time on set was short, but that doesn't necessarily indicate anything about the size of his role.
"What's interesting is that it's such a huge, sprawling cast and people seem to be there for ages, but they actually shoot two or three days and that's it," he said. "Once it's put together it looks like everybody must be there for weeks and weeks and weeks."
For Bradley, the past season of "Game of Thrones" was the most exciting for him. His character's central role in the infamous "Red Wedding" scene depicted in the penultimate episode "The Rains of Castamere," and has drawn an intense fan reaction due to the bloody death of several characters.
But Bradley relates more his own character than those the fans have connected with.
"I felt intense pleasure (killing them), which was alarming," Bradley said of watching the episode. "I'd do it all again if I had the chance. They got what was going to them!"
Bradley, who said he hasn't read George R.R. Martin's books that the show is based on, is filming the upcoming episodes, but he's uncertain of Walder Frey's fate beyond that.
"I don't know what the future is on 'Game of Thrones,' " Bradley said. "I was on Season 1 and I'm just finishing Season 3 and I'm moving on to Season 4 now, but whether I'll be thereabouts (going forward) I just don't know. It would be nice, but I just don't know yet."
Gatiss, best known for his role of Mycroft Holmes on BBC's "Sherlock" (he is also one of the creators), noted that he's prepared for the fan obsession that accompanies being on a TV show like "Game of Thrones."
"My life is entirely composed of fan obsession -- so this is just another one to add to it," Gatiss said. "It's all a Venn diagram."