Former NFL tight end Rob Gronkowski celebrates the IPO of Flutter EntertainmentSpencer Platt// Getty ImageFormer NFL star Rob Gronkowski's said his best investment ever was buying shares of Apple.In 2014, Gronkowski invested $69,000 in Apple. He said the investment is worth more than $600,000.Apple stock has surged 972% since the iPhone 6 was launched in 2014.Former NFL star Rob Gronkowski said the best investment move he ever made was buying Apple stock a decade ago.Gronkowski told Fortune that in 2014 he received the tip from his home builder to buy shares of Apple."The guy actually who built my house in Foxborough, he told me, 'Hey buy Apple stock.