The BBC confirmed today that Michelle Ryan (Eastenders, Bionic Woman) will be joining David Tennant in the next Doctor Who special, “Planet of the Dead.” Ryan will play play the mysterious Lady Christina de Souza, who “joins the Doctor on a bus-trip which takes a very unexpected detour into danger.”

Executive Producer and writer Russell T Davies further added, “As always the script is being kept strictly under wraps – however we can reveal that Lady Christina is a woman with a mysterious past who’s going to have a huge impact on the Doctor!”

Ryan has been rumored to be in the running for companion to the eleventh Doctor, Matt Smith, for series five in 2010. I suppose it will all depend on whether or not Lady Christina is left behind at the end of “Planet of the Dead” or continues with the Doctor in the TARDIS. On the other hand, it could be a test to see how popular she is. Remember that Catherine Tate’s Donna Noble appeared in a one-off appearance in the 2006 Christmas special before returning as a full-time companion for all of 2008’s series four. Time will tell and we will tell more as we find it out.