Millar, who served as Chairman of the then International Rugby Board (IRB) between 2003 and 2007, will be remembered as one of the sport’s finest statesmen, playing a major hand in the advancement of the sport on the global stage.

“We are deeply saddened to learn of his passing,” said Mr Mark Alexander, president of the South African Rugby Union (SARU).

“He touched many lives in his remarkable rugby career, and he will forever be remembered as a towering figure in rugby history.

“On behalf of the South African Rugby Union, we extend our heartfelt condolences to the Irish Rugby community, the Millar family, and to all who knew this remarkable icon of the sport.”

Dr Millar is credited with leading the reshaping of the game and presided over what will be regarded as the first modern men's Rugby World Cup in Australia in 2003, a landmark women's Rugby World Cup in Canada in 2006 and a record-breaking men's Rugby World Cup in France in 2007.

He was elected President of the Irish Rugby Football Union (IRFU) in 1995, a transformative time for the sport, and represented the union with distinction on the IRB Council from 1992, as well as serving as Chairman of the British & Irish Lions between 1999 and 2002.

Before success in the boardroom, Millar was one of the finest players, coaches and managers of his generation. A stalwart of Ballymena Rugby Club and Ulster Rugby, Millar made his Ireland debut in 1958 and won a total of 37 caps as well as playing on three British & Irish Lions tours in 1959, 1962 and 1966.

He went on to coach Ireland between 1973 and 1975 and led the Lions to an undefeated tour of South Africa in 1974. He also served as Lions manager on the 1980 tour and as Ireland manager at the inaugural Rugby World Cup in 1987, a tournament he had a deep passion for and one that would play a central role in his time as IRB Chairman.

World Rugby Chairman Sir Bill Beaumont led the tributes from the global rugby family. “I know that I speak on behalf of colleagues and the global rugby family when I say that Syd Millar was a giant of the game on the world stage.

“As influential in the boardroom as he was brilliant as a player, coach and manager, Syd was a natural leader and visionary, someone who cared deeply about the sport, its people, values and future.

“Syd led the sport through some of its most defining moments, driving forward the expansion and development of the sport beyond its heartlands. He was an inspiration to me, and many aspiring administrators, and he will be greatly missed.

“All our thoughts are with the Millar family and friends at this difficult time.”