Former Australia lock Dan Vickerman has died at the age of 37, the Australian Rugby Union (ARU) has confirmed.
South Africa-born Vickerman played 63 Tests for Australia after his 2002 debut and featured in three World Cups.
"The rugby world is in shock after news of the tragic passing of Dan Vickerman. He was an enforcer on the field and a much-loved character off the field," said ARU chief executive Bill Pulver.
No details of the cause of death have been disclosed.
The former Wallaby died at his family home in Sydney and is survived by wife Sarah and two sons.
He retired from the game in 2012 after spells with the Brumbies and Waratahs franchises in Super Rugby, and also spent the 2009-10 season in England with Premiership side Northampton Saints whilst studying at Cambridge University.
He played for Cambridge in their 2008 Varsity match defeat by Oxford, before captaining the Light Blues to victory in the 2009 edition at Twickenham.
England head coach Eddie Jones, who coached Australia and the Brumbies in his homeland, was among those to pay tribute.
"On behalf of the RFU and myself, I would like to send my condolences to Dan Vickerman's family, Sarah and the two kids," he said.
"He was a wonderfully committed team player and a good guy. He will be sorely missed by the rugby community."