The special has already confirmed the participation of Tenth Doctor David Tennant and current Eleventh Doctor Matt Smith, and showrunner Steven Moffat apparently reached out to Eccleston to join in the celebration as well.
Rumors circulated that Eccleston initially accepted the offer and then abruptly pulled out of the project, but U.K.’s Digital Spy is reporting that official BBC sources say Eccleston never agreed to be involved.
The site obtained the following quote from an “official source”: “Chris met with Steven Moffat a couple of times to talk about Steven’s plans for the Doctor Who 50th anniversary episode. After careful thought, Chris decided not to be in the episode. He wishes the team all the best.”
Eccleston played the Ninth Doctor for a single series in 2005, and was instrumental in helping to make the long-running show’s 21st Century re-launch an international success. At the time of his departure, Eccleston told the Yorkshire Evening Post that he “didn’t enjoy the environment and the culture that we, the cast and crew, had to work in” on the show. But that he felt the re-launch “broke the mold and it helped to reinvent [‘Doctor Who’]. I’m very proud of it.”
Additional cast members confirmed for the anniversary special include returning favorite Billie Piper (whose character, Rose, was the Ninth Doctor’s companion) and current companion Jenna-Louise Coleman as well as guest stars John Hurt and Joanna Page (“Gavin & Stacey”). While details are still under wraps, we have seen an image of Tennant and Smith at the official read through.