Ratko Mladic, the ruthless former Bosnian Serb military leader convicted of war crimes and genocide, was briefly hospitalised this week, his son told AFP on Friday.
Mladic, who is appealing his convictions by a UN court over the 1990s war in Bosnia, has been in fragile health after suffering several strokes.
Son Darko Mladic said his 76-year-old father felt unwell during a prison visit by his wife on Thursday.
"A doctor came to examine him and he was then hospitalised," the son told AFP, adding his father felt better on Friday and was returned to his cell in The Hague.
"I spoke to him on the phone... he is feeling well and is in good spirits," Darko Mladic said.
The family was awaiting official documents to explain what had ailed his father, said Mladic, adding it appeared to be nothing more than "the ailments he is already suffering".
Ratko Mladic has been dubbed the "Butcher of Bosnia" for the mass slaughter at the hands of his Bosnian Serb troops during the 1990s war that left 100,000 people dead and over two million displaced.
He was captured in 2011 and convicted by the International Criminal Tribunal for the Former Yugoslavia in 2017 of war crimes and genocide, notably over the mass killing of over 8,000 Muslim men and boys in Srebrenica in 1995.
He lodged an appeal in March 2018 and the case is still to be tied up.