The teenage defender, who first made a name for himself at Cork City at the age of just 16, joins after leaving AC Milan in the summer.

The Irishman had initially joined Milan on loan for the second half of the 2021/22 campaign before making a permanent switch to the San Siro the following summer.

After leaving the Italian giants, Heffernan earn a trial at Newcastle and featured twice for the U21 side in pre-season, and impressed enough to earn a deal with the Toon.

The youngster said: “It’s surreal to join such a big club like Newcastle. It’s definitely a club that is on the rise and with a lot of history. During the last week, I’ve been so excited to get started and I’m now looking forward to a big season ahead.

“The first thing I noticed when I arrived on trial was the lads were really welcoming and I just want to carry that on into the season, getting to know them more. The people of Newcastle are also really nice, too.

“I have become a much better defender during my time at AC Milan and I learned so many things to improve my game during my two seasons in Italy which should stand me in good stead for the future.

“The goal, when playing Academy football, is to try and break into a first-team as quick as you can and, hopefully, I can do that at Newcastle United.”

Heffernan will link up with United’s second-string ahead of Friday’s Premier League 2 trip to Reading and becomes Newcastle’s second summer signing at second-string level following the arrival of goalkeeper Reece Byrne from League of Ireland Premier Division side FC last month.