American Express is selling its exclusive Costco portfolio to Citi.
Last February, American Express announced the end of the exclusive co-branding agreement on grounds that it couldn't find a deal that made better economic sense. The end of the deal was slated for this March.
In a statement Monday, American Express confirmed that it has sold the portfolio to Citi. The sale is expected to close in June, and all Costco customers with co-branded American Express cards will be transferred to Citi.
American Express could earn up to $1 billion from the sale, according to the statement.
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The loss of the exclusive deal with Costco was seen as a huge blow to American Express, which also recently lost an agreement with JetBlue, and faced an antitrust lawsuit from the Department of Justice.
And in a CNBC interview Monday, Warren Buffett, the company's largest shareholder, said the loss of Costco was a "big deal".
He spoke about American Express after a viewer question that wondered why Berkshire Hathaway is still invested in the company even after all its recent issues.
Buffett noted that it's a very strong brand with a great reputation that will continue to face lots of competition.
American Express shares were little changed in pre-market trading.
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