David Bowie was set to return as FBI Agent Phillip Jeffries for a cameo but it didn't happen before the musician's death in January of 2016.
To avoid spoilers from leaking online, the cast were only given the scripts with their own lines on each day of shooting, after which they had to return the pages, which were then shredded under supervision.
Many original cast and crew members came out of retirement to work again on the series.