Sheppard was an instant hit with fans playing the role of Agent Canton Delaware III in the opening episodes of Series 6 The Impossible Astronaut and Day of the Moon, helping the Doctor to eliminate one of his creepiest foes – The Silence.
Sheppard said: "I grew up watching Doctor Who, and the fans are a huge part of what really makes the show so very special. I can't wait to come back to Cardiff for this unprecedented behind-the-scenes event - a unique chance for fans to meet the amazing people responsible for so much of the show we all love and get to experience their talent and creativity in a totally new way"
Also announced as joining the Convention line up today are: Nick Briggs, voice of the Daleks; Neil Gorton, A Director of effects specialist MillenniumFX; Ian McNeice who appeared as Winston Churchill in the Doctor Who episodes The Wedding of River Song; The Pandorica Opens; Victory of the Daleks and The Beast Below; and Raquel Cassidy who played Cleaves in The Almost People and The Rebel Flesh.
They join a host of cast and crew appearing at the Official Doctor Who Convention including: Matt Smith; Steven Moffat; Arthur Darvill; Danny Hargreaves; Tom MacRae; Barnaby Edwards; Caroline Henry; Stephen Pehrsson; Michael Pickwoad; Andy Pryor; Gary Russell and Marcus Wilson with further announcements to follow in the next two weeks. The Convention is a full day event that will reveal the inner workings of Doctor Who, showing the journey from script to screen: Live special effects and pyrotechnic demonstrations; prosthetic masterclasses and in-depth Q & A sessions with the makers of the show will give an unrivalled glimpse into the behind-the-scenes world of Doctor Who. For more information about the event and for tickets please visit: www.dwconvention.com.
The event will be held at the Millennium Centre in Cardiff on the 24th and 25th March 2012.
(Source: BBC Media Centre)