The Chief of Defence Forces, General Muhoozi Kainerugaba, has condemned opposition figure Kizza Besigye to death by hanging.
In a series of posts on X on January 16 - he has since deleted them -, Gen Muhoozi, said the “tree of traitors” awaits Besigye in Gulu.
"We will hang KB (the initials for Dr Besigye's name) on Heroes’ Day. That’s the best day for him to die,” said Muhoozi, who is also the First Son.
"And then we will arrest enybody who has ever spoke ill of Afande Saleh in government."
The Heroes' Day is marked on June 9 in Uganda. It was started to pay tribute to men and women who paid with their life during the protracted guerilla war that brought President Museveni to power in 1986.
Dr Besigye, a retired Colonel, was Mr Museveni's personal doctor and is widely credited with saving the lives of many of the fighters who had been shot - including Museveni's brother General Salim Saleh and former army chief turned opposition politician Maj Gen Mugisha Muntu.
Dr Besigye is currently facing controversial charges in the military court after he was picked up from Nairobi, Kenya, on November 16 and illegally extradited.
On Tuesday, the military court added the charge of treachery to the original illegal possession of firearms and endangering the security of the defence forces.
Treachery is punishable with death upon conviction according to the Ugandan laws.
Gen Muhoozi has divided opinions in the country and beyond with his controversial use of the social media where he indulges in political comments.
The Constitution and the UPDF Act bar active military officers from engaging in politics, including such commentary.
In the past, senior officers and bush war heroes such as Gen David Sejusa and Lt Gen Henry Tumukunde have been court martialled for statements made in the media while serving military officers.
In the recent past, however, Gen Muhoozi has threatened to capture Nairobi in two weeks, to invade Sudan and to deport the US Ambassador to Uganda.
But he had never said anything about Dr Besigye, who became his father's biggest political rival after criticising the trajectory the principles - for which they had gone to the bush - was taking back in 1999.
Besigye has since challenged Mr Museveni in the election four times. He lost each time and maintains the elections were always rigged.
The declaration by Gen Muhoozi has drawn immediate reactions from Besigye’s supporters and international human rights groups.
Before he quit X on January 10, he had taken to threatening to deform Opposition leader Robert Kyagulanyi.
Winnie Byanyima, Besigye’s wife and a prominent figure in her own right, condemned the military’s actions and the lack of legal fairness in her husband’s case.
In an emotional statement, Byanyima questioned the legitimacy of the military court, given that both President Museveni and his son Muhoozi hold significant control over the military judiciary system.
“President Museveni and his son run the army. The military court falls under them. Father and son are the accusers and the judges in the case against my husband,” Byanyima said, expressing her belief that the charges against Besigye and his associate, Obed Lutale, are politically motivated.
She further vowed to attend her husband’s trial, despite the lack of justice, and affirmed that she would honor Besigye’s legacy as a “true hero of Uganda and Africa” regardless of the outcome.