Paris Saint-Germain have completed the £4.2m signing of Alex from Chelsea.
Alex, who is believed to have signed a three-year deal, will link up with his former Blues boss Carlo Ancelotti in the French capital.
The Brazilian, 29, handed in a transfer request after slipping down the pecking order at Stamford Bridge following the arrivals of David Luiz and Gary Cahill.
"He is a great professional," said Ancelotti. "It was a good opportunity given his price."
He is PSG's second major signing during the January transfer window after full-back Maxwell joined from Barcelona.
Alex joined Chelsea from Santos in 2004 and was loaned to PSV Eindhoven from 2004 to 2007.
"He has a lot of experience because he played in the Dutch and English leagues and also with his national team," added Ancelotti.
Alex was unveiled as a Paris Saint-Germain player during a news conference on Friday at the Parc des Princes.