Mertesacker joined the Gunners in a £8million deal from Bremen on transfer deadline day.
Mertesacker admits he watched Arsenal’s 8-2 defeat at Manchester United on Sunday.
“I watched that game and I wasn’t too delighted,” the 26-year-old said.
“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.”
