Sunderland have completed the signing of Celtic fullback Adam Matthews.
The Black Cats confirmed the deal on Friday night, a little more than 24 hours after agreeing a fee with the Scottish champions.
Head coach Dick Advocaat said on the club's website: "We know that we need quality players to improve competition for places in the side, so Adam is a welcome addition to our squad and we are very pleased to welcome him to Sunderland.
The fee exchanging clubs is £2 million.
"Adam is a player we have been tracking for some time," Sunderland sporting director Lee Congleton said. "Even though he is only 23 years old, he has a wealth of experience, and I am sure he will continue to improve under the leadership of Dick Advocaat."