The 18-year-old full-back has made 33 first-team appearances and won three Wales caps since breaking into the Bluebirds first team in August last year.
The two clubs reached agreement over what is reported to be a £2million deal last week and the player underwent a medical over the weekend.
Copyright (c) PA Sport 2007, All Rights Reserved.
Do YOU want to write for GiveMeSport? Get started today by signing-up and submitting an article HERE: http://gms.to/writeforgms