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Fer's arrival at Carrow Road for an undisclosed fee is the second new signing to be unveiled by the Canaries in three days following the capture of Sweden international Martin Olsson from Blackburn.
The club's official Twitter feed read: "City can confirm Dutch international midfielder Leroy Fer has joined from FC Twente on a 4-year deal, subject to international clearance."
Fer and Olsson are two of a number of new arrivals at the club with manager Chris Hughton having been on a summer spending spree.
Fer's fellow Holland international Ricky van Wolfswinkel became the club's record capture at £8.5million while England Under-21 winger Nathan Redmond was last week purchased from Birmingham and defender Javier Garrido has signed permanently after a loan from Lazio.
Fer, 23, came through the youth ranks at Excelsior before he moved to Feyenoord, making his debut in December 2007 and establishing himself as a regular in the side the following season.
He became an integral part of the squad, earning widespread praise, before his move in 2011 to FC Twente and after further impressing there he was on the brink of a switch to Everton in January this year.
However, the transfer fell through after a knee problem arose during a medical and the clubs failed to agree on renegotiated terms.
Fer represented Holland at all levels from under-17 before making his bow in the senior team in the August 2010 friendly against Ukraine.
Fer then made his full senior debut against Turkey in a World Cup qualifier.