"I had a great time here last season so I'm really happy to be back," Ake told the club's official website.
"It's an exciting challenge. Chelsea is a great club and I learned so much there but this is a new step and the right place for me to develop even more," the Dutch international added.
Following the signings of Asmir Begovic and Jermain Defoe, Ake is Bournemouth's third major buy. According to ESPNFC sources, Ake's transfer was worth $25 million. Ake can play centre-back, left-back or as a defensive midfielder.
"The fans haven't seen the best of me yet. I always set the bar high so I know there is a lot of things I still have to work on. With the help of the manager here, I know I can keep improving and become a better player," Ake said.
Bournemouth manager Eddie Howe added: "I am delighted that we have completed the signing of Nathan on a permanent basis. He is someone we know all about, having had a very successful loan spell here last season.
"Nathan is an outstanding young player with a fantastic attitude and a great desire to learn and develop. He has a very bright future ahead of him and I'm very pleased to say that future is here."
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
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