Ajax have completed the signing of Holland Under-21 defender Mike van der Hoorn for an undisclosed fee from FC Utrecht.
The 20-year-old joins on a four-year contract which will keep him at the Amsterdam-based side until June 30, 2017.
Van der Hoorn told the club's official website: "I am very happy with this contract and am looking forward to starting training soon.
"I have signed a contract for four seasons. Ajax have been champions for the last three years so I hope that will continue.
"I hope to learn a lot from Frank de Boer and Jaap Stam, who in their time, were the best defenders in the world."