Current Doctor Who companion Jenna Coleman was scheduled to appear at Fan Expo Dallas (commonly referred to as just "Dallas Comic Con") earlier this year, but had to cancel due to a work commitment. I was sad, I'm not going to lie, but the folks at Dallas Comic Con managed to fix the problem pretty quickly: Coleman is among the first-announced celebrity guests for Dallas Comic Con Fan Days, which will take place at the Irving Convention Center October 16-18.
Other guests on the list so far are Jason Mamoa, who's known for Game of Thrones but will be Aquaman in upcoming DC Comics films (including, y'know, Aquaman); Ralph Macchio (The Karate Kid); John Rhys-Davies (The Lord of the Rings); James Marsters (Buffy the Vampire Slayer); Michael Rooker (The Walking Dead); Edward James Olmos (Battlestar Galactica); Aaron Ashmore (Smallville); Shawn Ashmore (X-Men); Bonnie Wright (Harry Potter); and Yaphet Kotto (Alien).
As is always the case, some of these names might have to cancel as the event gets closer and other names might be added/replaced, but overall it's a pretty solid list so far. I haven't quite fully recovered from Fan Expo Dallas back in May, but I might be fully energized again by the time October rolls around.