Australian rugby is mourning the death of former Wallabies lock Dan Vickerman at age 37.
The Australian Rugby Union confirmed that Vickerman died at his family home in Sydney overnight.
It is understood there were no suspicious circumstances.
He leaves behind a wife and two young children.
Born in South Africa, Vickerman moved to Australia at age 21 and went on to play 67 Tests and three World Cup tournaments for his adopted nation from 2002-2011 before injuries forced his retirement in 2012.
"The rugby world is in shock today after news of the tragic passing of Dan Vickerman," said ARU CEO Bill Pulver.
"Dan was an uncompromising competitor who forged a wonderful international rugby career despite a number of injury setbacks along the way.
"He was an enforcer on the field and a much-loved character off the field.
"He cared deeply about the game and the players, helping players transition into life after rugby in his role with RUPA following his retirement.
"Our thoughts and prayers are with Dan's family at this extremely difficult time."
Rugby Union Players Association CEO Ross Xenos said: "On behalf of all players, we extend our deepest sympathies to Dan's young family at this difficult time. We are truly shocked and united in our despair.
"Dan was universally respected by his peers and the rugby community during and beyond his playing days.
"Since retiring, he was very generous in giving back to the game through coaching and voluntary roles supporting players' off-field development.
"We encourage all players who are affected by today's terribly sad news to support and be there for each other and to contact RUPA if they would like to talk."
Vickerman linked with the Brumbies on arrival in Australia and made his Super Rugby debut in the 2001 season.
In June 2002 made his Test debut in a 31-25 Wallabies victory over France at Stadium Australia.
After three seasons and 33 appearances for the Brumbies, he was signed by the Waratahs in 2004 and played five seasons and 53 matches for them.
After playing in his second Rugby World Cup in France in 2007, Vickerman withdrew from Australian rugby for three years to study in England.
He earned a degree in land economics from Cambridge University, where he played in two Varsity matches against Oxford, captaining the side to a 31-27 victory in 2009.
He returned to Australia in time to earn selection by Wallabies coach Robbie Deans for the 2011 World Cup.
He played his last Test in the World Cup semi-final loss to eventual winners New Zealand at Eden Park.