David Tennant admits waving goodbye to his best loved character Doctor Who has been difficult. The actor, who has just finshed shooting his last scenes for the cult sci-fi drama, said: "It was quite emotional". He added: "Obviously it's filmed out of order, so the final scenes weren't the final scenes - which was probably lucky, because that may have been a little too emotional." The 38-year-old was in London with writer Russell T Davies for the launch of the second of four Doctor Who specials. The Waters of Mars will be broadcast on November 15. The Scottish star is keeping tight lipped about his departure from the cult sci-fi series. He hinted: "The structure of this episode is unlike anything we've ever done before. The Doctor finds himself in a situation where he knows what the end is."