Arsenal manager Arsene Wenger must plan for life next season without Mathieu Flamini.
The 24-year-old midfielder completed his move to AC Milan on Monday, agreeing a four-year contract with the Italian club.
Flamini, out of contract at the Emirates Stadium in the summer, underwent a medical and has reached an agreement over personal terms.
Milan vice-president Adriano Galliani revealed the signing was imminent after his team's 2-1 triumph over Inter in Sunday's derby.
Wenger admitted on Sunday he was not "super-confident" Flamini would still be at Arsenal next season.
Despite the offer of a lucrative new five-year deal - understood to be worth around £55,000-a-week - from the north London club, his head was turned by Milan's interest.
Juventus were also reported to be tracking the France international, who formed a fine partnership with Cesc Fabregas at the heart of the Arsenal team this season having seemed to have been on his way out of the club at the end of the last campaign.
He put in a fine performance at the San Siro as Wenger's team knocked Milan out of the Champions League at the last-16 stage in March.
The former Marseille man will compete for a place in Milan's midfield alongside Brazil star Kaka and Italy trio Gennaro Gattuso, Andrea Pirlo and Massimo Ambrosini.
Milan climbed into the final qualifying place for the Champions League on Sunday, leapfrogging Fiorentina who lost 2-1 at Cagliari.
Flamini's last match as an Arsenal player will be Sunday's Barclays Premier League trip to Sunderland, before he officially joins the Milan ranks on July 1.
Milan sporting director Ariedo Braida said: "I have to say Flamini was a player that Ancelotti really wanted and Milan is like a family, where decisions are made jointly."
