That's right, the 11th incarnation of the Doctor, the one and only Matt Smith!
Thought you outta know ;)
EXTRA SIDE NOTE: MCM Expo have stated on their forums "The first 100 people to purchase the new series’ DVD at the BBC Worldwide stand will receive a wristband for the signing at the venue’s Signing Hall." So it looks that he will only be attending FRIDAY and there will not be a "normal" signing, you will only be allowed this if you are one of the lucky first 100 to buy the DVD and receive a wristband.
I would imagine the panel will also be ticketed also, or even worse first come first in. It will however be shown for free online so if you miss the panel, never fear you won't be missing out!