Doc’s last line in Back to the Future 3 implied he had been to the future in his Time Train, and the comics have finally explained the story.

Back to the Future Part III ended with Doc’s line “Nope, already been there” and the comics have finally explained if he did, in fact, go back to the future in his Time Train. The final piece of the Back to the Future trilogy was released in 1990 and saw Doc and Marty (Christopher Lloyd and Michael J. Fox) navigating the Wild West. Doc and Marty wrestle with their tragic future fates and try to rectify them without causing too much damage to the timelines but threats from 1885 mean they struggle to even make it back alive. Since Back to the Future III, there has been a musical and comics but no more movies, leaving the film's conclusion somewhat mysterious.

Back to the Future Part III was filmed back-to-back with Back to the Future Part II as the story continues directly from its predecessor. The famous DeLorean is damaged and Doc’s clever thinking, and the timely invention of the steam train, allow them to get the time-traveling car back to speed. The end of Back to the Future Part III shows Doc and Marty reuniting when Doc turns up in 1985 in a time-traveling steam train. Doc’s final line, when asked by Marty if he is going to the future, is “Nope, already been there”, implying Doc and his family have been time traveling on many different adventures.

Doc's Finale Back To The Future 3 Line Was Intended As A Joke

Back to the Future’s plots all continue on from each other, creating one ongoing story and many different Back to the Future timelines. Doc’s final line in Back to the Future Part III implies this transition will continue and a fourth movie would focus on Doc’s journeys into the future on the Time Train. However, the Doc’s final line was meant as nothing more than a joke. The line harks back to the ending of Back to the Future which sees Doc and Marty heading off on another adventure.

Although the ending seems to perfectly move on to Back to the Future Part II, screenwriter Bob Gale revealed that they never had any plans for the second part until after the first’s success, as Back to the Future was expected to fail (via The Hollywood Reporter). Gale confirmed that Doc’s final line in Back to the Future II replicated this, and the hint of further adventures was simply showmanship and a joke between the time-traveling duo. Doc’s final line was a nod to the franchise story as a whole and a way to give a satisfying ending at the end of Back to the Future Part III, with the audience knowing the characters will be going on more adventures.

How Back To The Future Comics Explained Doc's Final Line

Back to the Future’s comics, Tales from the Time Train, continue the adventures of Doc Brown and focus on continuing to build the characters already in Back to the Future. Gale may have originally intended for Doc’s last line to only be a joke but the new comics mean the intentions of the line change for continuity reasons. Gale and comic co-writer John Barber wanted to continue Doc’s story with his family and knew Doc’s final line had to be the start of that story. If Doc had told Marty he had already been to the future before the ending of Back to the Future Part III, then the comics had to tell that story.

Back to the Future: Tales from the Time Train 1 is set just before the end of Back to the Future Part III and Doc has finally completed the Time Train. Doc and his family travel to 2038. After running into some trouble, Doc decides they need to be more secure and wants to leave. Clara suggests they run their errand first which is what brings them to October 1985 where they reunite with Marty and Jennifer. This is the ending moment of Back to the Future Part III and brings the audience up to speed about where in the future Doc had been traveling in the future, and what inspired his final line.

Source: The Hollywood Reporter