Ben Roberts-Smith, Australia's most highly decorated soldier, has been arrested over unspecified allegations of war crimes.
Federal police arrested the Victoria Cross-holder at Sydney Airport on Tuesday morning.
They, alongside the Office of the Special Investigator, said Mr Roberts-Smith was expected to be charged with "five counts of war crime - murder".
The maximum penalty for the offence is life imprisonment.
Officers were seen waiting at the arrivals gate as the decorated soldier's flight from Brisbane landed.
Mr Roberts-Smith holds both the Victoria Cross and the Medal for Gallantry, Australia's two highest military honours.
He has consistently denied any wrongdoing throughout years of legal proceedings related to his conduct during deployments in Afghanistan.
The arrest follows a lengthy legal battle against Nine newspapers and journalists Nick McKenzie and Chris Masters following their 2018 reports alleging he had committed war crimes.
Mr Roberts-Smith said their stories portrayed him as a criminal "who broke the moral and legal rules of military engagement" and "disgraced" his country and army.
He sued them for defamation, but the newspapers defended their reporting as true - including claims that Mr Roberts-Smith was complicit in murder.
Mr Roberts-Smith holds both the Victoria Cross and the Medal for Gallantry, Australia's two highest military honours
|GETTY
The case eventually fell against the decorated soldier in 2023, with Justice Anthony Besanko ruling that claims Mr Roberts-Smith murdered four unarmed Afghan civilians were substantially true.
Mr Roberts-Smith challenged that verdict, arguing insufficient evidence supported such serious findings.
But Australia's High Court rejected his appeal application last year.
That day, he was ordered to cover a portion of Nine's legal expenses from the failed appeal.
The combined costs of the 110-day trial and subsequent 10-day appeal are estimated to surpass $30million (£15million).
The 2018 newspaper articles contained graphic allegations about his conduct in Afghanistan.
LATEST FROM AUSTRALIA:
PICTURED: Ben Roberts-Smith leaves the Federal Court of Australia in Sydney in 2021
|GETTY
One claim said he kicked a handcuffed man off a cliff before ordering the prisoner's execution.
Another allegation accused him of machine-gunning a detainee and claimed he brought home the victim's prosthetic leg to use as a drinking vessel.
These were among the allegations Justice Besanko found to be substantially true in his 2023 ruling.
Roberts-Smith's High Court challenge argued the Federal Court erred by assuming he had accepted certain allegations that were not re-contested during his appeal.
The VC-winner was born in Perth in 1978 and enlisted in the Australian Regular Army in 1996.
He served two tours in East Timor with the Third Battalion, Royal Australian Regiment, before transferring to the Special Air Service Regiment in 2003.
His first Afghan deployment in 2006 earned him the Medal for Gallantry for his work as a patrol scout and sniper during Operation Slipper.
His Victoria Cross was awarded for actions during his fifth Afghan tour in June 2010.
He drew enemy fire to protect pinned-down patrol members before storming and silencing two machine-gun positions at close range.
Mr Roberts-Smith has maintained his innocence throughout all proceedings.