Reilly, who hails from Castleford, is rated as one of the sport’s finest-ever players and coaches, too, following a distinguished career in the game.
He won the Challenge Cup with his hometown as a 21-year-old in 1969 - also claiming the Lance Todd Trophy as man-of-the-match against Salford - and again the following year when they defeated Wigan.
A formidable loose forward, Reilly was a member of the Great Britain Lions team that won the Ashes in 1970 and starred with Australian club Manly Sea Eagles before returning to Castleford and coaching them to their last Challenge Cup glory in 1986.
Reilly, now 66, coached Great Britain from 1987 to 1994 and was also in charge of Leeds when they defeated Castleford in the 1988 Yorkshire Cup final.
He later led Newcastle Knights, with the brilliant Andrew Johns under his command, to their maiden Australian Grand Final success in 1997 and is revered both here and Down Under.
Reilly will be the chief guest at Wembley on Saturday welcoming the players from Castleford and Leeds before kick-off and, after watching the showpiece match from the Royal Box, will present the trophy to the winning team.
RFL Chief Executive Nigel Wood said: “We are delighted that Malcolm has accepted the invitation to be Chief Guest at the Tetley’s Challenge Cup final.
“With his strong connections to both clubs and proud record in Rugby League’s oldest and most prestigious knockout competition, Malcolm is a true Challenge Cup great.”
Reilly said: “I was thrilled to receive this invitation and had no hesitation in accepting. It’s a real honour to attend this fixture and I still have many close friends at both clubs.
“It is going to be a great game with plenty of outstanding players on display.”