- California Doubling: Paris was not considered as a filming location because over the decades, development had detracted from the grittier architecture wanted. Dublin was also considered before settling on the Czech Republic, which suffered little damage during the two world wars. Many historic buildings were intact and privately owned stately homes were rented for filming.
- Fake Nationality: Being a BBC production, inevitably all the main roles are played by British actors. Except Aramis who is played by a Venezuelan-born Chilean...so, not French in any case.
- McLeaned: Richelieu is killed off in the gap between the first and second seasons, due to Peter Capaldi leaving the show to play the Doctor in Doctor Who.
- Real-Life Relative: Father Duval from episode 1.06 is played by David Burke, father of Tom Burke who plays Athos.
- Relationship Voice Actor: In the Japanese dub, Mamoru Miyano (d'Artagnan) and Yūichi Nakamura (Aramis) worked together in Mobile Suit Gundam 00 as Setsuna F. Seiei and Graham Aker/Mr. Bushido respectively, except as enemies.
- Release Date Change: The series was originally planned to be broadcast in 2013, but was later delayed until 2014.
- Short Run in Peru: The entire third series was broadcast in certain Eastern European markets several weeks before the UK. Additionally all of the episodes of Series 3 were released on Hulu in the U.S. simultaneously, before some of them had premiered in the UK.
- What Could Have Been:
- The second season would have been very different if Peter Capaldi hadn't been cast in another show.
- Similarly, the third season was originally planned to have a lot more of Milady (and consequently, her redemption arc and relationship with Athos). Unfortunately, the actress was busy being very pregnant and then giving birth, so they only had her for five days of filming. To accommodate this, her role was changed to a one-episode HeelFace Turn.
Trivia / The Musketeers