Gerry Mallon said it's been a "really difficult decision" to leave his top role in charge of Ulster Bank in the Republic after less than two years.
In an interview in May's Ulster Business magazine, Mr Mallon, who formerly headed up Danske Bank, said he has "zero regrets" about taking up his post as chief of Ulster Bank in the Republic, and that it took some convincing to move to his new role with Tesco Bank.
Mr Mallon said that the banking environment in the Republic had been "interesting". However, he added that he was surprised by how negative the perception of the industry, and bankers in general, still is.
"It's a really difficult decision to leave RBS and to leave Ulster Bank," he said.
Speaking about his new role with Tesco Bank, the Belfast man - who is also chairman of the Irish Football Association (IFA) - said: "I wasn't interested in a move, and wasn't looking for a move.
"At that level, you get approached... I initially said that I wasn't interested, but Tesco persisted in asking me to take a look at it.
"Then the more I did, the more excited I became about it," he added.
Mr Mallon said he didn't expect to leave his top Ulster Bank role after less than two years in charge.
"Yes, clearly you don't go into a role like that with the expectation that you will leave in a couple of years," Mr Mallon commented.
"I did see myself as having a longer term at RBS, but when opportunities present themselves to you, you can't choose the timing," he said.
"I have zero regrets about the move to RBS, which I think has been wonderful development for me, and I am moving on to something which is a fantastic new opportunity."
The May issue of Ulster Business magazine is available now