"I trust myself and I trust the person who called me (chief executive Dong Ren). If I go it's because I haven't done my job properly," he said.

"We have the same aim and we know each other better every day.
If you're coming to a place where you think you can get success in two or three months I would have stayed at home. I'm full of confidence and energy.

"Since the first conversation I knew my time at home had finished. Dong demonstrated his passion, I felt I was waiting for that passion. After 18 months I knew I should choose the right job."

Blues approached Slavisa Jokanovic and old boss Chris Hughton, while they also spoke to ex-Wigan manager Paul Cook and former Leeds chief Paul Heckingbottom.

Karanka turned the club down in 2017, but chief executive Ren promised the former Real Madrid defender will be given time.

"Aitor turned us down before and that also tells you why he chose us this time. He has got everything, otherwise I wouldn't have gone there again," he said.

"I was looking for a partner, every decision will be made together. It's team-work.

"It's well documented we've had two significant sales in the last two windows (Jude Bellingham and Che Adams) and I'd be lying to say we haven't got anything in the chest. We will do what Aitor thinks is reasonable and he will have our backing.

"Aitor will have the time and authority to build and lead this club going forward. From the first call I said I am not looking for someone to work for me and the club, I'm looking for a proper partner to help this club move forward."

Birmingham will face Tottenham in a friendly on August 29, with Karanka meeting Jose Mourinho, who he worked with at Real Madrid.

And the former Nottingham Forest boss hinted he will be seeing if the Spurs manager can offer him any players.

"He called me to give me his congratulations when I arrived here," added Karanka. "When he was at Chelsea we took on loan good players (at Middlesbrough), let's see if he has some good players who can come."