NEW YORK, Oct 7 (Reuters) - Fifth Third CEO Tim

Spence said discussions to buy regional bank Comerica ( CMA )

started a few weeks ago when the latter company's CEO Curtis

Farmer called to discuss a deal, Spence told Reuters in an

interview on Tuesday.

Fifth Third announced an agreement on Monday to buy Comerica ( CMA )

in an all-stock deal valued at $10.9 billion. It was the biggest

U.S. bank deal of the year and would create the nation's

ninth-largest lender.