The 24-year old French midfielder has signed a five-year deal with Betis after just 18 months with the Black Cats.
N'Diaye initially joined Sunderland from Bursaspor in January 2013 before he was sent on loan to Eskisehirspor for the first half of the 2013/14 Turkish Super Lig season prior to joining Betis temporarily in January this year.
During his time at the Stadium of Light, once-capped Senegal international N'Diaye played just 16 times for the Black Cats.
Sunderland AFC (@SunderlandAFC) August 22, 2014
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