David Tennant was originally meant to return to 'Doctor Who' for a flashback episode.

David Tennant's original Doctor Who return looked very different

David Tennant's original Doctor Who return looked very different

The 52-year-old actor is back for three special episodes as part of the BBC show's 60th anniversary celebrations, and while he'll be playing the new Fourteenth Doctor rather than reprising his role as the Tenth, that wasn't always the case.

He told Radio Times magazine: "It would have been an unseen adventure from years before.

"[Showrunner Russell T. Davies] immediately had an idea for a story, which I’m not going to mention because I don’t think it’s yet seen the light of day.

"It certainly wouldn’t have been part of an ongoing story. But I hope one day he does use it, because it sounded great."

Initially, his comeback alongside Catherine Tate (Donna Noble) would have been set during season four, but the duo will instead return in new episodes 'The Star Beast', 'Wild Blue Yonder' and 'The Giggle'.

While the latter will mark the end of Tennant's latest run in the TARDIS as Ncuti Gatwa takes over as the Fifteenth Doctor.

However, he has admitted there is always a chance he could return in the future.

Speaking to SFX magazine, he recently said: "I think it would be disingenuous to imagine that I might never be asked again, because history would indicate that it was always a possibility.

"So I’m not going to say never because I don’t think anyone would believe me.

"That doesn’t mean I know that I ever will. But I suppose until I can’t run down a corridor it’s always a possibility. But I promise to have no plans."

Earlier this month, incoming star Ncuti admitted he "wasn’t able to enjoy" filming 'Doctor Who'.

He told the December/ January issue of British GQ: "It was annoying.

"I just wasn’t able to enjoy things anymore because [from the] outside, I can see that this is amazing, and oh, my God, you work with amazing people, and it’s a great opportunity, but I just felt like I was trying to get to the end, the finish line."