Alex Oxlade-Chamberlain left Arsenal after six years to join Premier League rival Liverpool for an initial fee of 35 million pounds ($45 million) on Thursday, the first high-profile move on the last day of Europe's transfer window.
The 24-year-old Oxlade-Chamberlain allowed his Arsenal contract to enter its final season after rejecting offers of a new deal, and had been linked with a move across London to Chelsea.
Facing the prospect of losing Oxlade-Chamberlain on a free transfer next year, Arsenal instead secured a big fee for the England international.
Liverpool announced the transfer, saying Oxlade-Chamberlain has signed a "long-term" deal.
Since joining Arsenal from Southampton in 2011, Oxlade-Chamberlain has won the FA Cup three times but hasn't come close to collecting a European trophy or winning the Premier League. He's joining a Liverpool side that is back in the Champions League and started the Premier League by winning seven points from a possible nine.
His 132nd and last game for Arsenal was a humiliating 4-0 loss — against Liverpool at Anfield on Sunday.
Oxlade-Chamberlain's departure from Arsenal is a further setback for manager Arsene Wenger, who has seen his side lose two of its opening three league matches.
"I rate him highly and he's one of the players who is on his way up," Wenger said earlier this month. "In the last year, he has made huge progress and I want him to stay here for a long time.
"I'm convinced he will be the English player that everybody will look at in the next two years."
At Liverpool, Oxlade-Chamberlain is likely to play as a midfielder — he was mostly used at wing back last season — but faces competition for starts with Jordan Henderson, Emre Can, Georginio Wijnaldum, James Milner and potentially Philippe Coutinho.