With an in-depth knowledge of the Doctor’s life, the giant head left much to the imagination as to how this could be.
At end of the series, Jack casually mentioned that his old nickname used to be The Face of Boe, stemming from his birthplace in the Boeshane Peninsula.
It was then that the Doctor and sidekick Martha Jones (Freema Agyeman), realised it must be Jack from the future.
Fans will know that the Captain can’t die, ever since Rose Tyler (Billie Piper) resurrected him in season one after he was exterminated by a Dalek.
source: express.co.uk