Doctor Who's 50th anniversary special episode would've looked very different if Christopher Eccleston's Ninth Doctor was involved. The long awaited "The Day of the Doctor" was a tour de force of all things Doctor Who and finally delved deep into the "Time War" mystery that had been simmering since the long-running science fiction series was first revived by Russell T. Davies in 2005. Teaming the then-current Doctor, Matt Smith, with his predecessor, David Tennant and John Hurt's War Doctor, the landmark episode explored the Doctor's morality and reintroduced Gallifrey to the franchise in an epic, dual-heart warming final act.

Former Doctor Who showrunner and "The Day of the Doctor" writer, Steven Moffat, has confirmed in interviews that his original intention was to have all of the modern Doctors involved: Smith, Tennant and the Ninth Doctor, Christopher Eccleston. Despite meeting with the highly-respected actor, Moffat was unable to convince Eccleston to take part. The Mancunian played Doctor Who's lead role for only a single season before departing under a considerable cloud. Eccleston cited issues with the BBC and Doctor Who's production as his motivation for leaving, claiming treatment of cast and crew was rife with inequality. Eccleston recently reaffirmed that the emotional toll of his original departure is what ultimately deterred him from taking up Moffat's offer to return in "The Day of the Doctor."

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Despite Eccleston's decision not to take part, some details regarding Moffat's plans for the Ninth Doctor have surfaced over the past 6 years and provided some idea of what was intended for the trio of familiar Time Lord faces. This basic premise of stopping both the Time War and a Zygon invasion would've remained in place, with the Doctor forced into deciding whether or not to use the ancient Gallifreyan weapon known as "the Moment" and eventually discovering that he didn't commit the atrocity he had spent years agonizing over. Here's how "The Day of the Doctor" would've changed if Christopher Eccleston had agreed to appear.

Switching The Ninth Doctor and The War Doctor

The War Doctor played by John Hurt

The most obvious difference is that the War Doctor wouldn't have appeared if Eccleston had signed on, as both he and Moffat have separately confirmed that John Hurt's character was a direct solution to the Ninth Doctor's absence. Most fans would agree that the wartime incarnation of the Doctor was a distinct highlight of the 50th anniversary special - sentiments echoed by Christopher Eccleston himself - and while losing John Hurt from the Time Lord's lineage might've made counting his regenerations a little easier, it also would've deprived the series of a much-needed fresh take on the iconic character.

In 2018, Steven Moffat released part of a draft script for Doctor Who's 50th anniversary episode that included scenes featuring the Ninth Doctor. The script reveals that instead of the War Doctor attempting to use the Moment to bring an end to the Time War, it would've been Nine wrestling with the moral conundrum. Considering Hurt's regeneration literally shed his "Doctor" title to carry out the mission, it might've been fascinating to see a regular version of the character attempt to make the same decision.

In a strange turn of events, some of the War Doctor's dialogue was actually taken directly from lines originally written for the Ninth Doctor. The moment when John Hurt tells Billie Piper "don't sit on that...it's not a chair, it's the most dangerous weapon in the universe" was initially intended as a line Christopher Eccleston would use. Typically, however, the Ninth Doctor in his Northern tones would've uttered, "it's not a chair, love."

Related: Why Matt Smith Left Doctor Who

The Ninth Doctor's Arc In "The Day Of The Doctor"

Matt Smith, John Hurt, and David Tennant in "The Day of the Doctor"

According to the draft scenes that have emerged in recent times, it's apparent that "The Day of the Doctor" would've featured a recently-regenerated Christopher Eccleston, who was still getting used to his new body. It's often speculated that the Ninth Doctor has only just changed form when debuting in "Rose," largely thanks to a few choice comments and a glance in a mirror. Moffat accounts for this in his novelization of the 50th anniversary special, where the Ninth Doctor destroys every mirror in the TARDIS so that he doesn't have to see his own face, consumed by the guilt of what he has supposedly done. Although this scene would've been incredibly dark, it could've been fascinating to watch play out on screen.

"The Day of the Doctor" storyboards by Andrew Wildman also provide a good idea of what the episode might've looked like with the Ninth Doctor's involvement. The drawings show the Doctor conversing with a "Raggedy girl" character in the same barn from the final episode, with the young girl strongly suggested to be the Moment's non-Billie Piper appearance. During this scene, the original script had the Ninth Doctor make several references to his very first episode, telling the girl to "run" and making fun of his own large ears.

Much like the War Doctor in the final edit, the storyboards depict Eccleston traveling through a time portal created by the Moment and landing in a forest. Upon arrival, however, the sketches show Nine confronted with David Tennant's Doctor cavorting alongside two Queen Elizabeths. In the finished episode, this is the scene that greets the Eleventh Doctor after his journey through the portal, whereas the War Doctor arrives a little later, just as Ten and Eleven are getting to know each other. While Matt Smith's reaction to his former regeneration's escapades is relatively laissez-faire, the exchange might've been very different if Eccleston's Ninth Doctor had been the one to find his successor messing around with a Queen of England and a Zygon. "Excuse me, would you mind not flirting while I save the world?"

Story Changes To "The Day Of The Doctor"

Paul McGann is The Doctor

Christopher Eccleston's inclusion in Doctor Who's 50th anniversary special (and John Hurt's subsequent omission) would've had a significant domino effect on other areas of the story. For instance, it's quite likely that the Moment wouldn't have been able to take the guise of Rose Tyler. Rose's return in "The Day of the Doctor" was only possible because she mostly interacted with John Hurt's Time Lord, to whom she had no personal connection. If the Ninth Doctor had been the one attempting to use the Moment, bringing back Billie Piper may not have been an option, since it would've created a whole new layer of guilt for the Ninth Doctor.

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Rose Tyler wouldn't have been the only casualty of the Ninth Doctor's appearance. Without the War Doctor, fans might never have witnessed the sublime "The Night of the Doctor" short film that returned Paul McGann to the franchise after years of anticipation - at least not in the same form. The entire thrust of the mini-episode was the Eighth Doctor giving in and finally joining the Time War by regenerating into John Hurt. However, if Eccleston was going to be freshly-regenerated in "The Day of the Doctor" then that angle couldn't have been used, since there's an implication McGann's Doctor died while actively participating in the Time War.

Undoubtedly, Eccleston's inclusion would've given the dynamic of the three featured Doctors a complete overhaul. In the finished episode, Tennant and Smith's relatively similar, youthful Doctors are treated almost as naughty, bickering schoolchildren by the wizened War Doctor. While Eccleston's grittier version of the character still might've found his two successors a little too exuberant, the smaller age gap would've given the Ninth Doctor less authority compared to the War Doctor. More importantly, Ten and Eleven both show a certain degree of fear when faced with their bearded wartime incarnation, and this allows John Hurt's regeneration to stand out as an anomaly, forging a strange and uneasy dynamic that is only resolved in the episode's final act. It's unlikely that the same relationship would've been generated with Nine, Ten and Eleven.

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Many fans were understandably disappointed when the Ninth Doctor didn't return for the 50th anniversary episode, even if Eccleston's personal reservations are entirely justified. However, there's no denying that Moffat and co. pulled off something even more special and, in true Doctor Who fashion, snatched victory from the jaws of defeat.

More: Doctor Who: Time Lord Regeneration Rules, Limits & Plot Holes Explained

Doctor Who season 12 premieres in 2020 on BBC and BBC America.