Former Australia, Brumbies and Waratahs lock Dan Vickerman has died at the age of 37, the Australian Rugby Union (ARU) has confirmed.
Vickerman played 63 Tests for the Wallabies, the last of which was the 2011 Rugby World Cup semi-final against New Zealand.
The South Africa-born lock died in Sydney overnight.
"The rugby world is in shock today after news of the tragic passing of Dan Vickerman," ARU chief executive Bill Pulver said.
"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 [Rugby Union Players' Association] following his retirement.
"Our thoughts and prayers are with Dan's family at this extremely difficult time."
Vickerman made his Super Rugby debut with Brumbies in 2001 before signing for Waratahs three years later.
In 2008, he left Australia for England to study at Cambridge University, before returning and re-joining Waratahs in 2011.
He retired due to injuries a year later. He leaves behind a wife and two children.