Alfred N'Diaye has completed his move to Real Betis, ending an 18-month spell at Sunderland.
The midfielder has signed a five-year contract with the Spanish club, having spent the second half of last season on loan with the team.
The 24-year-old told the club's website: "I was happy here and felt valued. I always said I would not mind playing with Betis in the Segunda but I'm also convinced that it will only be for one season."
Betis made just 16 appearances for the Premier League side after joining in Martin O'Neill's spell in charge in 2013.