Amazon.com is expected to announce tomorrow the acquisition of the parent company of Diapers.com, according to media reports.

The deal for privately held Quidsi, which also operates personal care products site Soap.com, is worth about $540 million, according to reports by Fortune and The Wall Street Journal. Quidsi co-founders Marc Lore and Vinnie Bharara will remain with Amazon under multi-year contracts, according to the reports.

The online retailer will pay $500 million in cash and assume $45 million in debt, according to a report today by the Journal. The price tag for the New Jersey-based parent company is about $200 million higher than its valuation following its latest round of venture funding, according to the Journal.

Representatives for Amazon and Quidsi did not immediately respond to requests for comment.

Quidsi announced in April it had closed a $20 million round of mezzanine financing led by Pinnacle Ventures, which followed $30 million in financing led by New Enterprise Associates in 2009.

The deal would be Amazon's largest since it acquired shoe retailer Zappos in 2009 for about $850 million.