http://tardisspoilers.blogspot.com/2010/07/arthur-darvill-gets-screen-credit.html
This first part is not too surprising:

This first part is not too surprising:
But this part is:Although its been speculated for a while now, and reported on by us, it has officially been confirmed to us that Arthur Darvill will be considered a full time companion from the Christmas special onwards, finally getting a screen credit for his role as Rory Williams.
Please oh please let this third companion be River!!...both companions will be travelling in the TARDIS at Christmas, with a third expected to join during series 6
