Nathan will officially join Mourinho’s side on July 1st.
He has passed a medical and agreed personal terms after being watched by a whole host of European clubs, including Manchester United.
The player himself was the first person the confirm a deal had been struck, posting it on his Instagram account two days ago.
Nathan said: “I am very happy to be joining Chelsea, the champions of England, and I hope I will be able to learn a lot and develop my game.”
The Brazilian will join up with his new team-mates ahead of next season and is likely to spend the pre-season with the first-team in order to get up to pace with things.
Whether Nathan will feature regularly next season for The Blues is not yet understood, but he could spend a season out on-loan in order to develop.