Roger Federer keeps his promise and surprises young fan from 2017 US Open press conference

After a polite introduction, Ahmad asked the former world number one: “You have been the most consistent player of all time. Can you please continue to play for eight, nine years so that I can play you when I go pro?”

But it didn't stop there. 'Zizou' wanted some assurances, so he challenged the 21-time Grand Slam winner further. "Is that a promise?” the youngster asked, before Federer responded: “Almost. Pinky promise.”

Well, you know what they say – a promise is a promise and five years on, Federer kept his word.

Ahmad, who is now one of the top young tennis talents in America, was invited to Zurich, Switzerland, alongside his coach for what he believed to be a training session.

What happened next is just brilliant. Check out the clip below.

What a great story, huh?

Zizou, who is only 11-years-old, was crowned the number one player in both singles and doubles in the US earlier this year after impressing on court.

The youngster took to Twitter after the video went viral. "When the GOAT makes a promise, he keeps it," he wrote.

"That’s what makes him such an idol. Thank you Mr. Federer, for the best day of my life, for these memories and I am forever grateful that you kept your pinky promise!” HAPPY BIRTHDAY G.O.A.T!"