A Zappos like purchase for the e-commerce giant.

“What Amazon fears most: Diapers” declared the cover of BusinessWeek earlier this fall. Now it’s clear that Amazon didn’t fear diapers, it just wanted them for itself. Fortune has learned that Amazon.com on Monday will announce that it has agreed to acquire Quidsi, the parent company of websites like Diapers.com and Soap.com. The purchase price is $540 million in cash, with Quidsi’s co-founders agreeing to multi-year employment contracts with Amazon (AMZN). The price tag is $200 million over what Quidsi was valued at in its latest round of venture financing.

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