Robert Pattinson and Stanislav Ianevski, who respectively portray Triwizard champions Cedric Diggory and Viktor Krum from Harry Potter and the Goblet of Fire, are confirmed to attend the UK's Collectormania Manchester G-Mex, alongside Avery Brooks of Star Trek, Ian Somerhalder of Lost and Andy Serkis of King Kong and Lord of the Rings.
Collectormania's website also confirms that Matthew Lewis (Neville Longbottom) and Tolga Safer (Karkaroff's Aide) will be in attendance. A mention of Roger Lloyd Pack (Barty Crouch) as a possible guest has been made, but is yet to be confirmed.
In addition to conducting an autograph signing session, the four confirmed Harry Potter actors abovementioned will participate at a talk (actual date and time to be announced).
Collectormania Manchester G-Mex takes place the weekend of February 11-12, 2006 at G-Mex Central Hall, Manchester, M2 3GX. Visit their website for additional information.
UPDATE: Our apologies for the lack of clarification. For those who inquired, Collectormania is a Sci-Fi/Fantasy Convention.