Over the past decade, star of ABC's "Shark Tank" Kevin O'Leary has invested millions of dollars in innovative companies pitched by promising entrepreneurs. He's invested in everything from padded underwear to glue, but for O'Leary, two particular companies stand out from the rest.

"I've had many, many successes on 'Shark Tank' and many, many failures. That's the nature of venture investing," O'Leary tells CNBC Make It. "But, I've had some really big winners.

"Plated, one of my deals, got sold to Albertsons, the grocery chain, for $300 million dollars. That's the biggest exit in 'Shark Tank' history," he told CNBC Make It in October.

That was a deal that almost didn't happen for O'Leary. Mark Cuban originally struck a deal with Plated in the 2014 episode of the show but it later fell apart. In a follow-up segment of "Beyond the Tank," O'Leary was impressed with the company's development and invested. It paid off, literally, with the sale in September 2017; O'Leary told CNBC Make It at the time that he made a 1,346 percent return on his investment.

The other big "Shark Tank" winner in O'Leary's portfolio is Groovebook from season 5, he says. The company was created by Brian and Julie Whiteman and is a photo-printing app subscription service. The company sold to Shutterfly for $14.5 million in November 2014. In the Tank, O'Leary and Cuban invested $150,000 total for 80 percent of licensing rights.

"The deal was only 18 months old" at the time of the sale, O'Leary says. "[The co-founders] became millionaires. That's a great outcome."

A decade in on "Shark Tank," O'Leary says the investors often have around 30 to 40 companies in their portfolios at any one time, with a third typically undergoing acquisition. Many of the "Shark Tank" companies that end up skyrocketing to success do so, in part, because of the exposure, he says.

"Shark Tank" has become "iconic," O'Leary says. "You can launch a business on there because millions of people watch it. That means your customer acquisition cost is zero."

Indeed, Groovebook and Plated both reportedly experienced a big bump in sales, post-Tank. Even companies that didn't get a deal on "Shark Tank," like protein pancake company Kodiak Cakes, have reported a significant spike in sales after the episode aired.

"The No. 1 reason companies go out of business when they're started is they're never able to get the cost of acquiring a customer [lower than that customer's] lifetime value," O'Leary says. "Another way of saying, they spend too much on advertising. When 'Shark Tank' is telling everybody about your product, you don't have to spend a lot on advertising. And that's the secret sauce."

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Disclosure: CNBC owns the exclusive off-network cable rights to "Shark Tank."