The former Napoli man is the direct replacement for Antonio Rudiger, who joined Real Madrid after his contract expired in the summer.
A couple of seasons ago, Koulibaly was strongly linked to Chelsea and Manchester City, but he decided against a move and stayed in Naples, a place he has called home since joining from Genk in 2014.
The 31-year-old defender made 317 appearances for Napoli and hopes that his connection with former Neapolitan teammate Jorginho and international colleague Mendy will help his integration in south-west London.
“When we were on vacation Edouard (Mendy) tested me and asked me if I wanted to come and Jorginho did the same, and so I think I have double pressure,” he explained, in his first appearance in front of the media as a Chelsea player.
“They are both really nice guys and I used to have some really nice moments with Jorginho at Napoli, and and he has helped me a lot.
“Together me and Jorginho won some nice matches together, so when Jorginho asked me to come to Chelsea I wasn’t sure if the owner wanted me.
“But after Jorginho, Edouard also started texting and asking me, as we won the AFCON together, and when I had the possibility to join him here at Chelsea I was very happy.
“Until the last week they were always speaking to me to know if I will come or not, and when I signed Edouard was so happy because our families can spend more time together.
“With Jorginho I missed him a lot because when he left Napoli I lost something and now I’m very happy to be here with him and everybody.”
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