And the English duo have maintained that relationship even though Lampard, now retired from soccer, is back in London.
"I speak to Jack all the time," Lampard told MLSsoccer.com. "I think there a lot of big things to come from Jack. I like him, he's a great lad, great ability."
Harrison showed that ability once again with the opening goal for NYCFC in their 2-0 win over rivals the New York Red Bulls on Saturday, his seventh tally of 2017 to go with four assists in his sophomore season.
A viewing party for the game was held at the Pilgrim Pub in Kennington, London, as part of Heineken Rivalry Week and Lampard was the guest of honor.
Great things are expected of Harrison and while Lampard has been in close contact with Football Association technical director Dan Ashworth since his retirement, he does not feel it is his place to put in a good word for his former protege over a possible England call-up.
"I think he will do it [gain international recognition] of his own accord. I don't think he needs me to tell anyone," Lampard adds. "I think everyone [at the FA] knows that he's there... so it will happen naturally."
Did he wish he was lacing up his boots for NYCFC at Red Bull Arena? "Yes and no. I'm enjoying retirement. I am asked a lot, 'Do I miss it?' Of course I miss it in certain moments. But I threw everything at my career and I loved my time in New York. But there is a beauty in sitting back and watching it as a fan and taking it in."
Lampard still follows NYCFC as much as he can – and also gets back to the Big Apple whenever he can with his wife Christine.
"I do watch them [on TV] – but unfortunately it can be quite late at night so I catch up the following morning," the 39-year-old said. "We fell in love with New York, it's almost become something of a second home. We've been back twice since and we'll go again before Christmas. We love it."