Sunderland have completed the signing of Celtic right-back Adam Matthews for a fee of £2 million.
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."
- Sunderland AFC (@SunderlandAFC) July 3, 2015
Matthews, who joined Celtic from Cardiff in 2011, had been linked with a number of clubs and at one point appeared set for a return to his native Wales.
He made 42 appearances for the Bhoys last season and picked up a fourth Scottish Premiership winners' medal in the process.
"Adam is a player we have been tracking for some time," Sunderland sporting director Lee Congerton 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."
The arrival of the Wales international continues a busy few days for the Wearside club, who completed a permanent deal for Liverpool defender Sebastian Coates on Wednesday night and then tied up key midfielder Lee Cattermole with a five-year contract extension.
In addition, they are reportedly interested in Zenit St. Petersburg defender and Belgium international Nicolas Lombaerts and Dutch striker Jeremain Lens of Dynamo Kiev.