Author Douglas Adams is best known for writing the famous novel and radio series, The Hitchhiker's Guide to the Galaxy.
Born in Cambridge in 1952 and educated in Essex, he returned to Cambridge to study at St John's College.
Talking about Adams, Hearn said: "This was Douglas Adams' world, of course, because he'd been a student at St John's in the early 70s.
"You can still go to St John's and look at his archive, and you could see even when he was a student and before that, he was actually writing Doctor Who stories, even before he was a professional writer."
With 'Shada' being set in and around the University of Cambridge, Hearn added: "Ironically, St John's didn't actually grant the BBC permission to shoot there and so they had to shoot at Emmanuel and Clare instead."
Richard Bignell, author of Doctor Who on Location, said crews also spent time at Grantchester Meadow
"They obviously did a little bit of improvisation as well because when the Doctor first emerges from the TARDIS when it lands, he points out, 'mind that cow pat'," he added.
In 1983, the show celebrated its 20th anniversary. The producer wanted to reunite all the previous Doctors in a special episode called 'The Five Doctors.' However, Baker declined.
Hearn said: "The BBC very much wanted Tom Baker to be in the show, because it was a big feature-length 20th anniversary TV movie, and then somebody remembered that they had these fragments of this incomplete story in the archive.
"So they went back to the archive, found the bits of Shada, which of course had never been broadcast, and then wrote a story around these fragments and cut them into this TV movie."
36 years after the storyline was abandoned, Baker and the cast finally returned to complete Shada.
Baker and Lalla Ward, who played Romana, recorded the missing lines from Adams' original script, and the visuals were created with animation. This new, partially animated version was released in 2017.
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