Hakim Ziyech has officially signed a five-year deal with Chelsea after agreeing the terms of his arrival from Ajax, the Blues have confirmed.
The Morocco international's move to Stamford Bridge was announced earlier this month after Frank Lampard's side paid a €40 million (£33.5m/$43.3m) fee to acquire the 26-year-old's services.
Ziyech wll spend the rest of the current campaign in the Eredivisie, before making the switch to London at the close of the season.
"I am delighted and proud to have signed for such a huge club as Chelsea," the attacking midfielder told the club's website.