(Spoiler alert!)
If you though that nothing in 'The Nun' would be able to give you a shock, then you need to think again, the film's ending shows the exciting way in which it connects to the Warrens' universe, showing the origins of Maurice Theriault's possession, the person we see being exorcised in the original film, 'The Conjuring'. Despite this twist appearing at the end of the film, diehard fans of the franchise might have been able to guess this connection from the very beginning: Frenchy (Jonas Bloquet) is in fact Maurice Theriault.
The film is set in 1952 and tells the story of a Catholic Priest (Demian Bichir) and trainee nun (Taissa Farmiga) as they investigate the suicide of a Romanian nun in the Abbey of St Carta, with the help of a local farmer named Frenchy. Eventually we learn the truth about the alleged suicide; in reality it was a self-sacrifice in order to avoid possession by the demon Valak (to whom we are first introduced in 'The Conjuring 2'). The Priest, Father Burke, trainee nun, Sister Irene, and Frenchy come up with a plan in order to defeat Valak (who is the eponymous "nun") using the blood of Christ in order to cast the demon out and then attempt to seal the gateway to hell. Valak fights back and strangles Frenchy almost to death until Sister Irene saves him by spitting the blood of Christ (which she was hiding in her mouth) into the face of the demon. The ending appears to be a happy one, with Valak seemingly cast out and all others saved until, however, Frenchy reveals his real name, Maurice Theriault.
Peter Safran, the producer of 'The Nun' and of 'The Conjuring' saga explained how this idea came to him, saying that he likes "to feel that it's a cohesive universe, and we feel like these movies do organically fit together. And it's something that we don't try to jerry-rig it, you know. They all make sense. So when we started talking about what the movie 'The Nun' would be, and we said it would be that origin story of Valak, the demon, we always wanted to make sure that it was connected to 'The Conjuring' Universe, not simply by the fact that the character appeared in 'Conjuring 2', but that there really was a tangible string that exists for it. And one of the stories that we always loved is the Maurice story, the Maurice Theriault story".
Maurice, whose case was based on a real event in the 1970s, was an integral character not only in 'The Nun', but in both Conjuring Films and Safran admitted that he "really just thought it was a great, truthfully, just a really fun suggest for people...some of people will put it all together back from the first Conjuring that this was the character that we were talking about way back then".
The Final Scene in The Nun
It is the final scene in this film which truly underpins the connection between 'The Conjuring' universe and 'The Nun'; once Frenchy (or rather Maurice) awakes after Sister Irene seemingly saves his life, the happy ending is crushed when we see an upside-down cross on his neck and a flashback to Valak possessing him. The universes are then explicitly united when the film then cuts to the scene from the original Conjuring, in which Ed Warren discusses the case of Maurice's possession, referring to the demonic possession of the French-Canadian farmer.
