Iraqi monarchist Sharif Ali bin Al Hussein, a cousin of Iraq’s last king, Faisal II, died late on Monday.
Al Hussein, who was 66, had actively supported the opposition against former Iraqi president Saddam Hussein.
He had sought to re-establish the monarchy, which was deposed in a bloody coup in 1958, and continued his efforts after the 2003 US led-invasion. But the push to restore Iraq's royal family never generated widespread support.
“With great sadness and pain, we received the news of the death of Sharif Ali bin Al Hussein, the descendant of the Hashemite Royal Family, recalling his patriotic stances and contributions in the various stages of the struggle to get rid of tyranny and defend the rights of the Iraqi people,” Mr Salih said on Twitter.
“My deepest condolences to the Hashemite family and the Iraqi people, we ask God Almighty to bless him with his vast mercy,” he said.
Mr Al Kadhimi said he offered “condolences to the Hashemite family on the death of the prominent national figure, the patron of the constitutional monarchy movement”.
“We remember his legacy for his nationalism to create a democratic Iraqi state,” he said.
The Iraqi royal died in Jordan from a health-related issue. He has three children.
He led the Constitutional Monarchy Movement – an Iraqi opposition party – in exile, before returning to his homeland in 2003.
The party changed its name to the Constitutional Movement in 2010. Princess Badiya, a survivor of the bloody 1958 coup that ended her family’s rule in Iraq, was the mother of Al Hussein.
She died in London in 2020, where she had lived in exile. She was the last of Iraq’s princesses.