Former Arsenal captain William Gallas has completed his move to arch-rivals Tottenham Hotspur on a one-year deal, the club have confirmed.
Gallas, out of contract after leaving the Gunners in the summer, had only to complete a medical and agree personal terms.
Spurs have also retained the right to extend the contract of the 33-year-old, who also played in the Premier League for Chelsea, for another season.
Gallas will join a select band of players who have turned out for Arsenal and Tottenham and the move is likely to be controversial with some fans of both north London rivals.
Sol Campbell suffered terrible abuse after allowing his Spurs contract to run down and defecting to Arsenal on a free transfer in 2001. Tottenham fans have still not forgiven the former England defender.
But Spurs boss Harry Redknapp said on Friday: "It's all cobblers. What's he [Gallas] done? It's not the Yorkshire Ripper I'm signing, is it? He's a footballer, he plays football.''
Tottenham full-back Benoit Assou-Ekotto also said he had no problem with the club signing an ex-Gunner. "Look, Darth Vader could come to Spurs. I don't care," he said. "If he does his job well I am happy for Spurs."
France international Gallas was part of the Chelsea side which won back-to-back Premier League titles after moving from Marseille. He joined Arsenal in 2006 and captained the team in the 2007-08 season.