I know we have touched on this previously, but some new information has come to light so we thought we would dedicate some more time to this possible spoiler.
Basically, we have just recieved an email stating that the hunt is on for an actor to play a third companion to the Doctor alongside Karen and Arthur during series 6. Not much information is known at the moment except for the fact that the character will be male and should appear full time from the middle of S6.
The email also goes on to speculate that the new companion will possibly be from the past and will stay on into S7 after Amy and Rory leave the TARDIS. Again, we need to point out that this is just speculation at the time being, but as soon as we know more we will let you know.