The Duffer Brothers started filming the Stranger Things finale before they had finished the script because they were so "low on time"

In new documentary One Last Adventure: The Making of Stranger Things 5, Matt explained: "It's not like we don't know what the ending is. It's all plotted out. I have to write it, and we're just low on time."

Production assistant Montana Maniscalco was later seen saying: "We are shooting episode eight, which isn't completely written yet - spoiler alert! So we don't even fully know what's going on."

Matt then explained: "I've never read 8 through, and we're just shooting it. I've never done anything like this before. This is so weird jumping to eight ... Don't love it. Don't love it."

He went on to add: "We were getting hammered by production and by Netflix for episode eight. We went into production without having a finished script for the finale. That was scary because we wanted to get it right. It was the most important script of the season ...

"It was the most difficult writing circumstances we've ever found ourselves in, not just because there was the pressure of we had to make sure the script was good, but there's never been so much noise at the same time."

However, the writer/director/creator explained writing the final installment of the show was a tough feat, adding: "[It] was the longest time we've ever spent with the writers on a single episode."

One Last Adventure debuted on Netflix on Monday (12.01.26) and follows the cast from the first table read through to the last day on set as well as showing how the team filmed some of the big action sequences.

However, the documentary does not feature either Winona Ryder or David Harbour and director Martina Radwan was recently forced to explain their absence.

She told Variety: "We just didn't get the time. They were busy with other projects, and so we didn't have the time to sit down ... Unfortunately, with David and Winona, we couldn't find the time. We tried."