Thank the TARDIS, Doctor Who fans. It looks like Sci Fi won't let too much time pass between the third and fourth seasons here in the States. The cabler today announced that it had acquired Doctor Who 's fourth season and spinoff series The Sarah Jane Adventures . Both series will launch in April on Sci Fi. The fourth season of Doctor Who will feature David Tennant as the 10th Doctor in his third go-around (again, reason for celebration); he'll be joined by Catherine Tate 's Donna Noble, who reprises her role as the uppity companion from her previous appearance in the Doctor Who Christmas Special entitled "Runaway Bride." Fans of Freema Agyeman's Doctor Martha Jones, however, won't have to fret. Agyeman, after a recurring stint on Season Two of spinoff Torchwood , will rejoin the Doctor in the middle of the fourth season. "We are excited to have Doctor Who back on Sci Fi for its 4th season," said Chris Regina, Vice President of Programming