Fee: €8.6 million
The transfer puts to an end weeks of speculation surrounding the future of the out-of-favour custodian at the Estadio da Luz.
Roberto joined Benfica from Atletico Madrid last summer for €8.5m, but a string of disappointing performances throughout the season made him a target of the fans' rage.
The Spaniard's exit had been suggested for several weeks following the signings of Artur Moraes and Eduardo, but it was initially reported that he would leave the club on loan.
He will now return to the outfit he represented in the second half of the 2009-10 season on loan, during which he helped the side avoid relegation to the Segunda Division.