David Bradley is set to reprise his role as William Hartnell's first Time Lord in the 'Doctor Who' Christmas special
The 75-year-old actor played the original titular character in 'An Adventure in Space and Time' - the docu-drama to celebrate 50 years of 'Doctor Who' following William's death and now he will jump back into his old role to help current time-travelling scientist Peter Capaldi complete his last task before heregenerates.
An insider told The Daily Mirror newspaper: "David was convincing as Hartnell, it's exciting he's back.
"Four years ago it took all the previous Doctor's to save Gallifrey, so maybe some of the others will also pop up in Capaldi's swansong.
"It's great that the first Doctor will be there to help out during those all-important regeneration moments."
Capaldi has announced this is his last series as the Time Lord and is set to regenerate at the end of the year.
David, who is known for starring as Argus Filch in the Harry Potter series, played Hartnell's Doctor back in 2013 alongside the current Doctor at the time Matt Smith.
Hartnell played the character between 1963 to 1966 but died in 1975.
Last week rumours began suggesting Capaldi will regenerate into 'My Family' actor Kris Marshall.
A source said at the time: "Kris Marshall has already joined the cast and will regenerate at the end of this series, not the in the Christmas special."
However, a spokesperson for the BBC told MailOnline: "No casting decisions have yet been made on series 11."
The latest series started last Saturday (15.04.2017) and the Doctor's new openly gay companion Bill Potts, played by Pearl Mackie, was praised.
Pearl, 29, said; "I think it's crucial to have that kind of representation in mainstream TV, on shows that are aimed at children as well as adults."
It has not been confirmed whether Pearl will be leaving the series along with Capaldi at the end of the year.