Doug Mack, CEO of web-only home furnishings and décor retailer One Kings Lane, is leaving to lead web-only sports gear seller Fanatics Inc., according to an e-mail One Kings Lane sent to its staffers late this afternoon. Fanatics confirms the news, adding that Mack’s new role will be effective starting on April 21. He will be replacing Fanatics founder and CEO Alan Trager, who led the company for almost two decades, Fanatics says. Trager will remain on the board of directors.

“I’ve known Doug for more than a decade and can’t think of anyone better suited to lead the company’s next phase of growth,” says Michael Rubin, Fanatics’ executive chairman. “He brings the technology, marketing and customer-experience expertise to build Fanatics into a global multi-billion dollar enterprise.”

Chief operating officer and chief financial officer Dinesh Lathi will take over as CEO at One Kings Lane until the retailer selects a replacement, it says.

“Doug joined us in June of 2010 when we were 15 months new. At that point in time, we were on a great trajectory with solid footing, and Doug partnered with us to scale this business to an unprecedented place,” write One Kings Lane co-founders Susan Feldman and Alison Pincus in the e-mail. “His business acumen, belief in the One Kings Lane brand and commitment to our future contributed enormously to get us where we are today. We wish Doug only the very best as he takes on his new venture.”

A spokeswoman for the retailer says Mack’s departure will not change One Kings Lane’s plans, other than to move Lathi temporarily into the CEO role.

Trager had initially planned to depart from Fanatics in 2011 when he sold Fanatics to e-commerce technology and services provider GSI Commerce, now part of eBay Enterprise, a Fanatics spokeswoman says. “But GSI CEO Michael Rubin asked him to stay on to oversee the integration of Fanatics and GSI’s licensed sports business, especially after buying back Fanatics as part of GSI’s sale to eBay,” she explains. Rubin then asked Trager to stay in order to lead the acquisition and subsequent integration of Dreams Inc. and its FansEdge businesses in 2012. Now, at last, she says Trager “feels it’s the perfect time to retire because the integration is complete and the right successor was found.”

“As a life-long sports fan, I never imagined that I would have the chance to combine my personal love of sports with my passion for building great Internet companies, making Fanatics a dream opportunity,” Mack says. “By investing in and innovating every aspect of the customer experience, we will continue to revolutionize the way fans buy team gear.”  

One Kings Lane, which launched in 2009, reported $200 million in 2012 sales, putting it at No. 120 in the 2013  Internet Retailer Top 500 Guide. In January, it raised $112 million in its fifth funding round.

Fanatics is No. 43 in the Top 500 Guide. It booked 2012 web sales of $764 million, up 45.5% from $525 million the prior year. In the last year, Fanatics has made key hires to build out its e-commerce, m-commerce and merchandising teams.