The BBC plans to roll out all the stops for its Doctor Who 50th anniversary special, and it’s bringing back stars David Tennant and Billie Piper to help mark the occasion. Fans of the longrunning series are well acquainted with Tennant, who portrayed the show’s tenth doctor for three full seasons and various one-off specials. He passed the reins to current star Matt Smith in 2010; Smith will also take part in the 50th anniversary special set to air sometime this fall. Billie Piper took on the role of Rose Tyler, the doctor’s traveling companion for two seasons following Who’s 2005 reboot.