The attacking midfielder flew into London for talks in April and reportedly passed a medical.
And a move now seems guaranteed, with Nathan posting pictures on his Instagram account and changing his account bio to reflect he plays for Chelsea.
“A dream is coming true!” he said.
“First of all I want to thank God for always lighting my way, my dad who always believed in my talent and was a real warrior while helping me to reach my goals, my family and friends who always supported me...
“And I am also thankful to Club Atletico Paranaense, which was part of this journey and where I played for 6 years of my career. Thank you Chelsea for trusting in me, I will do my best to support my team on reaching new achievements. WE ARE ALL BLUE.”
source:eurosport