Sunderland have signed Gabon international midfielder Didier Ndong from Lorient for £13.6m (16m euros).
The 22-year-old has signed a five-year deal at the Stadium of Light after 18 months at the French club.
The fee is the highest Sunderland have paid up front for a player.
“I am excited to meet everyone at the club, to see the stadium and of course the fans, who I have heard so many good things about. Today is the most beautiful day of my life,” he said.
“Maybe the Sunderland fans don’t know me yet, but I promise they will quickly discover that I will give everything for them and the club.”
The upfront fee surpasses the £13m Sunderland paid for Asamoah Gyan in 2010, but the deal that brought Steven Fletcher to the club in 2012 included add-ons potentially taking the cost to £14m.
Ndong started his career at Tunisian side CS Sfaxien, playing 40 games, before signing for Lorient in January 2015 and making 46 appearances for the Ligue 1 club.
He has 18 caps for Gabon after making his debut in 2012.