In a short post on Twitter, the club wrote: 'City are delighted to announce the signing of Brazilian midfielder Douglas Luiz #WelcomeDouglas'.
He is the second Brazilian to join Manchester City in less than a year after the arrival of striker Gabriel Jesus from Palmeiras in January.
However, it's understood that he will be loaned out to Spanish side Girona for the 2017-18 season, although neither club has confirmed that move, and City say they will make a statement on his future "in the coming days".
U.S. probes China firm over North
Huang said coal imports dropped by three-quarters in the first half, and all those shipments had been made before February 18. North Korean traders in the country are banned from opening accounts at local Chinese banks.
Rail service between New Jersey-New York back after delay
The first train's passengers were provided snacks and water, and power was restored in about an hour, the Amtrak spokesman said. An Amtrak train stalled in a Hudson River tunnel caused delays into and out of Penn Station on Saturday afternoon.