It wasn't enough that director James Wan had to mourn the death of one of his film's biggest stars halfway through filming — he also had to find the strength to finish the movie and then figure out how to do it.

Macey J. Foronda for BuzzFeed Director James Wan

On Nov. 30, 2013, filmmaker James Wan was enjoying the first relaxing Saturday he'd had in many, many weeks. He was about halfway through directing Furious 7, his first time working on the multibillion-dollar movie franchise. And Universal Pictures' aggressive plan to release the film just 13 months after its predecessor set box office records for the Fast & Furious series meant Wan, his cast, and his crew had barely had a moment's rest as they pushed through shooting as much footage as they could on the film's Atlanta set. Wan was more accustomed to the low-budget horror movies — Saw, Insidious, The Conjuring — on which he’d built his career, and the Thanksgiving break finally afforded him a chance to breathe and spend time with friends and family. He was having such a great time, actually, that he didn’t notice that his phone's battery had run out. Then he got back home and plugged it in. "When the phone came back on, it just blew up with all these messages," a hunched over Wan told BuzzFeed News in his publicist's Los Angeles office. They struck an ominous tone: "Is this for real?" "Did this really happen?" "Is Paul OK?" "At first I thought this is another one of those internet hoaxes that you get all the time on social media," he said. "I'm like, this is a horrible, horrible joke, whoever's playing this." But then Wan noticed he had missed calls from Universal executives, and Fast & Furious franchise producer Neal Moritz. "My heart sank. I knew something really bad was up."

Scott Garfield / Universal Pictures Paul Walker

It was. Paul Walker, who played former undercover cop Brian O'Conner in all but one film in the Fast & Furious franchise, had died that day in a car accident after an event for his charity organization Reach Out Worldwide. He was just 40 years old. "When I got the news, I literally slid down the wall,” Wan said. “I just broke down. I could not believe that that happened. I was just in total, total shock." In the ensuing days, the most Wan and Universal could do was to agree to suspend production on the film. Whether they would ever return at all, Wan said, remained undetermined out of respect for Walker. "I actually want to give credit to the studio for not jumping at that," Wan said. "Because they were just as shocked. They truly loved Paul. It hit everyone really hard. We truly did not talk about finishing the movie until Paul was buried and we had a memorial for him. It was in the following weeks that we started thinking if this was something that we could actually finish without him."

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Ultimately, Wan, Universal, Moritz, and the rest of the Furious 7 cast agreed they really had no choice but to finish the film. After mourning his friend and colleague, Wan had to pick himself up and then, somehow, he had to get back to work. "I didn't feel I had to necessarily finish this movie for the sake of finishing this movie," said Wan. "I, like everyone else, felt like we had to finish this movie for Paul.” There is practically no precedent in modern Hollywood for the impossible dilemma the director was facing. The closest example is probably the accidental death of actor Brandon Lee in 1993 on the set of The Crow, but Lee, the film's star, reportedly had three more days left of filming. Furious 7, by contrast, was just halfway done. And, as Wan pointed out, The Crow's shadowy aesthetic and Lee's long hair and painted face made obscuring anyone doubling for the actor relatively straightforward. The opposite was true of Walker’s character. "The Fast and Furious franchise takes place in a world that is very bright, very happy," said Wan. "There was no way I could hide him."

Scott Garfield / Universal Pictures Tyrese Gibson, Michelle Rodriguez, Walker, and Chris "Ludacris" Bridges in Furious 7.

For Wan, however, the hardest part of finishing Furious 7 wasn’t in those technicalities. "For me, the most daunting part was the idea of waking up every morning, getting back on set, rallying the troops, and getting all the cast and all the crew back to making this movie," Wan said, half sighing, half laughing. "Just the idea of that made it so hard to continue with it." But they knew that had to do it — for Walker. “It became our obligation to finish this movie as a tribute to honor his memories and his legacy,” Wan said. “That became our number one goal when we picked up the pieces and we went back to work." The first step in picking up the pieces was figuring out how much footage he had of Walker. Before the film went back into production in April 2014 — Universal pushed the release date from July 11, 2014 to April 3, 2015 — Wan and his post-production team spent months poring over every scrap of footage that had ever been shot of Walker for 2009's Fast & Furious (the fourth in the series), 2011's Fast Five, 2013's Fast & Furious 6, and what Wan had already shot of Walker in Furious 7. "We had to look for … little nuances that he would make, so that we could possibly tell our visual animators, 'Well, when Paul says a line like this, he would look more like that,'" said Wan. "We literally had to build a bible, so to speak, that we could reference. Oh, when Paul is happy, he does this. When he's sad, he does this. It was so meticulous."

Scott Garfield / Universal Pictures Walker and Vin Diesel in Furious 7.

Working with screenwriter Chris Morgan, Wan then reshaped the movie's plot to fit every shot of and every line from Walker they knew they had, and then they planned how each of those elements would be incorporated into what Wan would shoot on the set. "[It was] probably more meticulous than anything we've had to plan for this film," said Wan. "And this movie has incredibly detailed action sequences and visual effects sequences." To double for Walker, the production turned to his younger brothers Caleb and Cody, as well as actor John Brotherton (who also has a separate role in the film). Visual effects artists then replaced their faces with Paul Walker's face — but occasionally, Brian O'Connor's lines would be a hybrid of multiple voices. "Sometimes, we would use the brothers to say certain lines, because we wouldn't necessarily have 'Archive Paul' saying that," said Wan. "So we may have the brothers saying one or two lines here, and Paul would finish off the sentence. It was this incredible jigsaw puzzle that we had to put together. I mean, Paul had a very distinct way of speaking. [Cody and Caleb] have the mannerisms, but they don't sound quite like Paul. So there's a lot of tweakage that we had to do. It really is a combination of so many different techniques and different methods to make it work."

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Wan declined to go into specific detail about what scenes involved this level of complex digital sleight-of-hand. "We don't want you to go, 'Oh, yeah, that looks kind of bad,'" he said. "We worked very hard so you don't have to be picking it apart." But once Wan finally got into the editing room to assemble the film, he said he tried to use every possible second of footage that he had shot of Walker for Furious 7. "One thing I realized as I was putting it all together was everything I had shot with Paul for this movie became so precious," he said. "Because I didn't have enough stuff with him, everything I do have with him became like gold that I just cannot let go." One example: Wan confirmed that Walker does appear in one of Furious 7’s most affecting — and eerie — scenes, when Brian has a phone conversation with Mia (Jordana Brewster), his series-long romantic interest, as he prepares for the final confrontation with the film's villains Deckard (Jason Statham) and Jakande (Djimon Hounsou), bracing her for the possibility he may not come back from it alive.

Peter Iovino / Universal Pictures Jordana Brewster in Furious 7.

"It was very difficult, obviously," he said. "We have to be sensitive to what happened. We're very mindful of [how] people watching this movie would feel. I will say that is my favorite scene in the whole movie. There are many cool action scenes in this whole film, but that scene says a lot about who Paul's character is. It says a lot about his relationship with Mia. And I just love how emotional it is." The scene is also a perfect example of one of the most emotionally taxing challenges Wan faced making Furious 7, because Brewster, who had missed much of the first half of production filming her (since canceled) TNT drama Dallas, shot her side of that phone conversation after Walker had died. "It was a tough one for Jordana," said Wan. "For her to try to do the dialogue with him and he's no longer there — it was just so hard. … I think Jordana was the most emotional through it all. It was doubly surreal when she had to do her scenes with Cody or Caleb, or with John, but pretend that it's Paul. That was a tricky one for me to direct, because I had to be very sensitive to that and just help her along and just try to get her in the right mindset." So much of the appeal of the Fast & Furious franchise, on screen and off, is wrapped up in the theme of family, both by blood and by choice. That added yet another heartrending strain to any scene in which cast members had to act as if their friend Walker was still there — no more so than for the franchise's paterfamilias Vin Diesel. "One thing that I never realized is how much Vin did look up to Paul," said Wan. "He would bounce a lot of ideas off Paul. … They shared so many scenes and moments together." But Diesel's familiarity with Walker also meant he could help Wan breathe more of the late actor back into his scenes. "Vin actually helped me fill in a lot of gaps," said Wan. "A lot of times he would say, 'You know, James, the way this is scripted now, Paul wouldn't do that. Paul would maybe say it more like this.' It was really cool to have that."

Jaimie Trueblood / Universal Pictures Wan and Diesel on the set of Furious 7.