Serena Williams and Alexis Ohanian keep their start-up investments 'separate' — even though they're married

When tennis legend Serena Williams and Reddit co-founder Alexis Ohanian first met at a cafe in Italy in 2015, the conversation quickly turned to business.

Today, the duo is married — with a daughter, Alexis Olympia Ohanian Jr. — and both have built sizable reputations as start-up investors. But Williams says they try to keep their business ventures apart.

"One of our first conversations was investing, because I've been investing for over nine years now," Williams told CNBC's "Squawk Box" on Tuesday. "We try to keep business separate. Obviously, there are things that come up, where we talk about business at home — but we try to keep our businesses as separate as they can be."

Still, Williams said, it's nice to have someone like Ohanian — who launched Reddit in 2006 alongside co-founder Steve Huffman, and then sold it to Condé Nast for $10 million 16 months later — as a resource and sounding board.

On Tuesday, Williams announced a $111 million fundraise for her new early-stage investment firm, Serena Ventures, saying she plans to invest in founders with diverse points of view. According to the firm's website, Serena Ventures has invested in 61 companies since launching in 2014, including home fitness company Tonal, cryptocurrency resource CoinTracker and Impossible Foods.

"The venture capital ecosystem really needs an inclusive player, and a player with a platform," Williams told CNBC.

Last year, Ohanian launched his own venture capital fund, Seven Seven Six — which has invested in 39 companies, according to the fund's website, including Angel City Football Club, a Los Angeles-based National Women's Soccer League expansion team. Ohanian has also invested in Impossible Foods, separately from Williams.

Ohanian and Williams are both bullish on cryptocurrencies, too. Williams told CNBC that investing in cryptocurrencies was a no-brainer for her, and she wished she'd jumped in sooner. "You have to really think outside the box when you're into [venture capital]," she said.

Experts caution people to learn and understand the risks before investing in cryptocurrencies, rather than simply buying into the hype. Many deem cryptocurrencies to be a volatile and speculative bet, and advise people to only invest as much as they can afford to lose.

Last year, Ohanian also told CNBC Make It that Williams helped him find a stronger work-life balance after they got married. "She was like, 'You work more than I do," Ohanian said. "And at first I was so flattered. I was like, 'Wow, thank you so much.'"

But Williams told him that it "wasn't a compliment," explaining that overworking is "not actually the way to sustained greatness." People need time to recover and regroup, "otherwise you can't be your best for a long time," she told him.

Since then, Ohanian said, he's been very disciplined with his time, particularly prioritizing family time.

"We can't do our best unless we have those resetting moments," he said.

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