Russell T. Davies has now confirmed (on BBC Breakfast) that Wilfred Mott, Donna's grandfather played by the always excellent Bernard Cribbins, will be returning as the Doctor's companion for David Tennant's last two episodes.
This is fantastic news! I loved Wilf in Season 4, especially in his heart-breaking last scene with the Doctor after Donna's memory had been erased. I have been saying for a while now that the producers ought to change up the Doctor/companion dynamic beyond the older Doctor/wide-eyed lady combination they've had going for the past few seasons - although, to be fair, Donna was a bit of a departure from that as well. I could really see Doctor #10 and Wilf working well as a team.
And just imagine if Wilf sticks around post-regeneration. How interesting would it be to have the youngest Doctor ever paired up with the oldest companion ever? That combination could really shake up the expected dynamic, perhaps putting the Doctor in a position where he actually asks for his companion's advice and wisdom on occasion. In short:
In a completely non-sexual way, of course. Although, this is Russell T. Davies.....