Swedish fintech firm Klarna will be the exclusive provider of buy now, pay later loans for Walmart, taking a coveted partnership away from rival Affirm, CNBC has learned.

Affirm shares are tumbling after rival Klarna, which is preparing to go public in the U.S., said it is now the exclusive provider of Buy Now, Pay Later loans for Walmart.

Klarna said it will become the exclusive buy-now-pay-later provider at Walmart in the U.S., replacing rival Affirm as the Swedish fintech company nears a potential initial public offering.