The 26-year-old 6ft 6in defender was allowed leave from the international training camp to complete his deadline day transfer from Werder Bremen, in what is understood to be an £8million deal.

Mertesacker and Brazil full-back Andre Santos, who arrived from Fenerbahce, will add some much-needed experience to an Arsenal backline which was brutally exposed at Old Trafford on Sunday, when England striker Wayne Rooney helped himself to a hat-trick.

The German has followed the Gunners since he was a teenager, and revealed the debacle against United did not make easy viewing.

"I watched that game and I wasn't too delighted," Mertesacker said from Germany's training camp in Dusseldorf.

"When I was young and visited England with my auntie, as somebody who was football crazy, I simply had to come back with a shirt.

"I can't remember why, but I came back with an Arsenal shirt and my brother had a Manchester United one.

"This affinity has grown over more than 10 years and now the loop closes because I am delighted to finally get to play at a team I always supported and where I always wanted to appear eventually."

Mertesacker continued: "I think Arsenal had been watching me for a while and had intended to sign me for a while.

"It was a strange situation for me because it was not clear for a long time what would happen and it dragged out to the very end.

"After the medical in London (on Tuesday), it took until late yesterday and I was unsure it would work out, but then I was delighted in the end.

"It is a dream come true and it is a very attractive challenge."

Wenger was busy in the final days of the transfer window, having brought in South Korea captain Park Chu-young from Monaco earlier in the week.

The £10million signing of Mikel Arteta from Everton was completed just ahead of the deadline, along with a season-long loan move for Israel captain Yossi Benayoun from Chelsea.

The 29-year-old Spaniard is reported to have taken a pay cut to agree a four-year deal at the Emirates Stadium.

Arteta will strengthen a midfield ripped apart by the departures of skipper Cesc Fabregas and Samir Nasri.

The transfer offers Arteta the chance to test himself at another level.

"It is a big challenge, a different challenge, fresh for me and I want to see myself on the biggest stage, the Champions League," he said on evertontv.

"I am 29 years old, so I haven't got much time left to take a chance like this one."

Santos, 28, joins the Gunners from the Turkish champions, and the Brazil international intends to win more silverware as soon as possible.

The defender told ArsenalPlayer: "There are great expectations from the supporters and I hope that my way of working, of playing, will win the hearts and minds of the other players, the supporters and all those who work for Arsenal.

"This is my main goal at the club - I managed to win over the supporters at Fenerbahce and I hope the same will happen here."

Santos added: "I arrive here with one aim - being a champion.

"I will wear Arsenal's shirt and give my utmost to it. I will do everything for the club."

Sunderland, meanwhile, could consider making a permanent move for Nicklas Bendtner next summer, should the Denmark forward impress during his season loan at the Stadium of Light, in another move with was pushed through just ahead of the transfer deadline.