The 801st episode of Doctor Who airs on BBC1 (the 103rd episode since the series’ revival). This is the show’s 50th anniversary special, starring Matt Smith, David Tennant, and John Hurt, with past Doctors putting in appearances via archive footage; Tennant’s co-star Billie Piper also appears, though not as Rose Tyler. This is the first episode since 1976 to feature the shape-shifting Zygons, and it adds a major plot twist to the Time War. 
Big Finish Productions