Arsenal have confirmed that Gilberto has completed his move to Panathinaikos.
The Brazil international midfielder has been a stalwart of the Arsenal side since arriving in London from Atletico Mineiro in 2002.
He featured heavily in 2003/04 as the Gunners won the Premier League title without losing a single game to become branded as the 'Invincibles'.
The emergence of Mathieu Flamini last season meant that Gilberto was no longer a regular starter, but he still took his tally of appearances to 244.
Flamini left Emirates Stadium to join AC Milan at the end of last season but Arsene Wenger informed Gilberto that he still could not be guaranteed first team football.
That prompted the 31-year-old to look elsewhere and he flew to Greece earlier this week to discuss a move to Panathinaikos.
He was offered a lucrative three-year deal and Arsenal have now announced that the transfer has been finalised.
Arsenal also thanked Gilberto for his 'huge contribution' to the club on their official website and wished him the very best for the future.
Gilberto's exit comes just 24 hours after Alexander Hleb sealed a switch to Barcelona.