In 2014, when Gronkowski was playing for the New England Patriots, he was having a 4,486-square-foot house built in Foxborough, Mass., about 20 miles outside Boston. The contractor Gronkowski hired gave the tight end, who was then 25 years old, some valuable investment advice. 

“Every time I saw him, when we were building the house, he kept saying, ‘Get Apple. Get Apple,’” Gronkowski tells Fortune in an exclusive interview alongside Julian Edelman, his former Patriots teammate and current cohost on the Dudes on Dudes podcast. “So after the 50th time, I got it. And let me tell you, it’s the best investment I’ve ever had in my life.” 

At the time Gronkowski, or Gronk as he’s known in the football world, was just four years into his playing career. While making millions from his NFL contracts and endorsement deals, he was a novice in financial matters. 

“I [had] never been involved in stocks,” Gronkowski says. “I really didn’t know how stocks work. So I was like, ‘All right, let me do this, man.’”

After the advice from the helpful homebuilder, Gronkowski decided to “go big.” The amount he invested was in keeping with his persona of a lovable jock. 

“Obviously this just fits along the lines of just me being myself; I’m going to put $69,000 into Apple stock,” Gronkowski says. “So I call up my financial advisor. I’m like, ‘Put $69,000 in Apple.’ My own money, with no advice like this, is just from the guy who built my house here in the New England area.” 

Gronkowski actually ended up forgetting he’d even invested the money until about two and a half years later, he says. By the time he remembered he’d squirreled away the money, his $69,000 investment had more than tripled to $250,000. He promptly sold a portion of his Apple stock and kept the rest. 

“Now to this day, I have over $600,000 in Apple stock, all because of the investment I made in 2014 having no idea what I was doing, but just listening to the guy that built my house here in New England,” Gronkowski says. 

Circa 2014, the year of Gronkowski’s investment, was a marquee year for Apple. The tech giant started the year with a horrendous first quarter that had investors fretting the company had lost its mojo after the death of iconic founder Steve Jobs. The next quarter, the stock clobbered analyst expectations, soared 8% in a day, and continued the climb to becoming the most valuable company in the world. (Earlier this month, Nvidia overtook Apple as the world’s most valuable company.)   

Over the course of his 11 seasons in the NFL, Gronkowski made roughly $70 million in salary. Despite his well-documented party-boy lifestyle, he famously never spent any of his salary, according to his 2015 autobiography It’s Good to Be Gronk. Instead, Gronkowski lived off his endorsement money from brand deals with the likes of Dunkin’ Donuts, T-Mobile, and USAA. 

Now that he is retired, Gronkowski has several business ventures that keep him occupied. He has a media company, Nuthouse Sports, alongside Edelman, his friend of 15 years, and marketing executive Assaf Swissa, who founded the ad agency Superdigital. Gronkowski is also a coinvestor in a chain of salad restaurants called Greenlane with Tory Burch founder J. Christopher Burch. 

But so far, no investment has paid Gronkowski back like the Apple shares his contractor recommended. 

“Let me tell you, he built my house, and he gave all the money back to me by telling me to invest in Apple,” Gronkowski says.