Striker Danny Welbeck says he had pictured himself playing in the Arsenal team while still at Manchester United and "couldn't be happier" after his move to the London club.
The 23-year-old joined the Gunners for £16m on transfer deadline day.
He had been with the Old Trafford club since the age of eight.
But he told Arsenal's club website: "I've envisaged myself playing in this team before. For it to finally happen is very exciting."
Welbeck broke into the United first team in 2008 and went on to start 53 Premier League games, with a further 39 appearances from the bench.
However, his first-team chances became limited under Louis van Gaal, who was appointed United manager in May, and he started just one game for the club this season - the 4-0 defeat by MK Dons in the second round of the League Cup last week.
"I've been at United ever since I was a little boy and I had a great time there," Welbeck added.
"I just think this is the next stage of my development - to come to Arsenal, to really show people what I can do as a footballer and hopefully get to the place where I want to be.
"I really do believe that coming to Arsenal is the right decision."
Mike Phelan, who was Sir Alex Ferguson's assistant at United between 2008 and 2013, felt Welbeck's departure had broken part of the club's identity.
|Former Manchester United coach Mike Phelan:|
|"Someone like a Danny Welbeck has been part of United's identity and that has been broken."What will happen in the future now, nobody knows, but that thread has been broken now."|
But Phelan also said Arsenal was the right move for Welbeck, and expects the England international to be able to play in his preferred position as a striker.
The move will also see the England forward play alongside international team-mates Jack Wilshere, Theo Walcott, Kieran Gibbs, Alex Oxlade-Chamberlain and Calum Chambers.
"I believe that with the manager's style of play and with the magnificent players in midfield slotting balls through, I can run on to the end of those balls and put them away," said Welbeck.
"I'd like to bring pace and power to the game. At Arsenal, we're not short of combination football and I like to join in on that and get in behind defenders and try to get shots on goal.
"I want to score some goals and help the team to achieve the right results."