Filming almost took place at the end of 2016, but Robert Downey Jr. wasn't able due to his commitment to the Marvel franchise.
Robert Downey Jr. has been looking at Johnny Depp for an unspecified role
The choice of Arsene Lupin as an antagonist came from the Maurice Leblanc novel where Sherlock Holmes and Lupin had crossed paths.
In April 2021, Robert Downey Jr. posted a clip on Instagram of him working on martial arts moves with a trainer. It said, "First Reel?! Here we go! Here's a couple weeks back with Sifu Eric Oram! #WorkoutDowneyJr." He didn't say if it was for a movie role, but many fans started wondering if he has finally starting production on this film.