Former NFL superstar tight end Rob Gronkowski revealed that his shares in tech giant Apple have proven to be his "best investment" to date.

The NFL legend said he bought Apple stock on a tip from his home builder over a decade ago, and had forgotten about the investment for years.

Super Bowl champion Rob Gronkowski says he received a valuable piece of investing advice in his 20s from "the man who built my house."

Warren Buffett's Berkshire Hathaway ( BRK.A -0.24%) ( BRK.B -0.15%) stock portfolio is one of the world's most closely followed collections of stocks. The reason is simple: Buffett has led Berkshire to market-crushing gains over a long period of time. A $1,000 investment in Berkshire Hathaway at its IPO would be worth $2.4 million today.

Famed tight end Rob Gronkowski made millions from his NFL years but the best investment return he saw was from Apple stock he forgot he'd bought.

Former NFL tight end Rob Gronkowski explained how his "best investment" came from a stranger building his home

There is one stock he has never sold since buying in 1991, though: American Express (NYSE: AXP). Buffett owns over 20% of the credit card issuer and bank, making it the second-largest position in the Berkshire Hathaway portfolio. The position trades at a value of $40 billion as of this writing.

NFL legend Rob Gronkowski has revealed how a $69,000 (£54,000) investment in Apple stock, made solely on his house contractor's advice in 2014, has now ballooned to more than $600,000 (£473,000). The former New England Patriots star made the investment despite having no prior knowledge of how the stock market worked.

Former All-Pro tight end Rob Gronkowski made a good amount of money during his NFL career and it's helped him branch out into some very successful post-career ventures. But there's one investment he made during his playing career that he's particularly proud of.