New Delhi, Nov. 10 -- Tom Grogan, a 35-year-old entrepreneur, became a multimillionaire after selling a majority stake in Wingstop UK to a US-based private equity firm in a deal valued at £400 million ($532 million). Yet he says he has failed to find joy in early retirement and plans to return to work.

After nearly a decade of building the UK brand from scratch - from sending a cold email to Texas and facing 50 investor rejections to finally opening 57 restaurants - Tom Grogan told Fortune that navigating life after the sale has been an entirely different challenge.

"It's all you think about. And then when you get there, it's just a bit surreal. It's like, Okay, it's done now. Now what? And money doesn't necessarily fill that void ...