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The following story contains MINOR SPOILERS for the third season of BBC's "Doctor Who."

Get ready to suspend your disbelief.

For those who saw the first part of "Doctor Who's" second season finale on BBC last weekend, "Army of Ghosts," you've already met the Doctor's (David Tennant) new companion. Well, kind of.

In what is considered to be an interesting move if nothing else, BBS announced that Freema Agyeman will join the cast of "Doctor Who" for the show's third season as new companion Martha Jones. Agyeman, however, is no stranger to viewers of "Doctor Who." In fact, she appeared in the most recent episode of "Doctor Who" as a totally different character, Adeola, who met an untimely fate as an employee of the Torchwood Institute. Executive Producer Russell T. Davies said the casting of Agyeman as the new companion may result in some confusion, but the benefits of having her with the Doctor far outweighed any negatives.

"The search for a new companion has been underway for some time when I first saw Freema Agyeman, she had come in audition for the part of Adeola in (season) two," Davies told BBC. "Watching her during filming confirmed what an exciting new talent she was so, under cover of darkness, we called her back to audition with David for the role of the new companion. It was an immediate and sensational combination, and her range, presence and charm blew us all away."

Agyeman said she has known for months about her new role on the show, and it's been excruciating keeping her lips sealed.

"I've been keeping this secret from my friends for months ... it's driving me mad," the 27-year-old actress told BBC. "Auditioning with David in secret down in Cardiff was unbelievable, but I never in my wildest dreams thought I'd actually become the new companion."

Agyeman is practically a newcomer to television, according to Internet Movie Database. She's appeared in a few British series including "The Bill" as Shakira Washington, "Silent Witness" as Mary Ogden and "Casualty @ Holby City" as Kate Hindley. She will replace singer Billie Piper, who played Rose Tyler in the first two seasons of the show. It's been foreshadowed that her character will die in the season finale, set to air in England next weekend, but it's unclear what the actual fate of her character will be. Piper left the show after the second season.

"Billie rightfully built up an amazing fan base and she will be missed, but I hope the fans are willing to go on new adventures with me," Agyeman said.

"The first scripts have been written, and Martha's a brilliant addition to the Tardis crew, the perfect foil for the Doctor," Davies said.

Agyeman will not actually make her debut until the real start of Season 3, which means she will not appear in the annual Christmas special, Davies said. "We've got another surprise for that," he said.

"Freema was a joy to work with in Episode 12 of the current series. She is not only very talented and very beautiful, she's great fun and I'm delighted she's coming on board the Tardis full time," Tennant told BBC. "I wan't wait to welcome her into the Who family."

Filming for the third season begins this summer in Wales, with 13 new episodes beginning again around Christmas time for BBC One.

The second season of "Doctor Who" is expected to air on SciFi Channel in the United States this fall. Reports have the show being paired with the third season of "Battlestar Galactica," both which have been major ratings winners for the cable channel.