His adviser, Abdallah Othman Abdurrahim, also confirmed his death but without giving details. "Seif al-Islam has fallen as a martyr," his cousin, Hamid Kadhafi, has told Libyan TV. Emerging reports point to what appears an assassination.

Four unidentified men reportedly entered his property and shot him in a garden execution-style. "Four armed men stormed the residence of Seif al-Islam Kadhafi after disabling surveillance cameras, then executed him," according to a statement. There have long been reports and rumors that he was attempting a return to national politics after previously being barred from any top office.

The killing took place in Zintan, in northwestern Libya - though he had long kept himself hidden from public view amid Libya's fractured politics and current state of internecine civil war. He's said to have been based in Zintan for much of the last decade.

Despite never holding an official post, the younger Gaddafi effectively served as his father's number two from 2000 until 2011, operating as a key power broker inside Libya until Muammar Gaddafi was overthrown and killed by by NATO-backed Islamist 'rebels' - bringing an end to decades of stable rule.

It was on October 20th 2011 that Col. Gaddafi was dragged from a drain pipe outside his hometown of Sirte, tortured and killed. He was sodomized with a bayonet, before being shot - with much of the brutal death captured on grainy cell phone footage. Western officials celebrated the war crime and summary execution.

His son Saif was captured in 2011 while attempting to flee the country and was subsequently imprisoned in Zintan. He remained in detention for years before being released in 2017 under a general amnesty, and quietly returned to living in Libya, but at times was in and out of the news, also as competing powers vied to form a new government.

Al Jazeera reviews of Saif's life and background:

A Western-educated and well-spoken man, Gaddafi presented a progressive face to the oppressive Libyan regime run by his father – and he played a leading role in a drive to repair Libya's relations with the West, beginning in the early 2000s.

He received a PhD from the London School of Economics (LSE) in 2008, with his dissertation looking into the role of civil society in reforming global governance.