Alan Shearer, Franco Baresi and Paolo Maldini are among the players confirmed for the match on 11 September.
Proceeds from the game will benefit The Great North Children's Hospital, Sir Bobby Robson Foundation and Newcastle United Foundation.
"I'm honoured such a great team is coming," Harper told BBC Newcastle.
"We're going to be privileged to see some of the greatest players to ever play the game. If you picked an all-time world XI then Franco Baresi and Paolo Maldini would certainly be in a lot of people's teams.
"To have that iconic AC Milan team that I grew up watching on a Sunday is fantastic."