André Hanekom, 61, the South African man who was held in Mozambique since August last year, has died in custody in Pemba in that country.
Hanekom's daughter, Amanda, confirmed Hanekom's passing to News24.
"He died on Wednesday morning," Amanda said.
Hanekom's daughter said he had been transported to Pemba ahead of his court appearance on terrorism charges and a meeting with the high commissioner on Friday when he suddenly and inexplicably took ill.
"We are hoping to recover my father's remains in order to determine the cause of death," Amanda told News24.
"He was taken to hospital in a critical condition and admitted to ICU. My mother, Francis, was allowed to visit him and said he was recovering well. [On Tuesday] he was able to sit upright and use his muscles, but this morning he passed away."
According to Amanda, hospital officials said Hanekom was struggling to breathe.
"My father had always been the rock of our family," a tearful Amanda told News24. "He had suffered so many setbacks in life; yet, he always persevered.
"He was a strong man, this is a heavy blow to us," she said.
Amanda said the last picture Francis took of André showed that he had suffered considerable weight loss while in custody.
"He looked terrible. This is terrible..."
Hanekom, a business owner from Palma, who had lived in Mozambique for 26 years, was first allegedly abducted from the parking lot of the Amarula Hotel just north of Palma in August last year by four men wearing balaclavas.
He was reportedly shot with an AK-47 assault rifle during the incident and driven off in a brown Land Cruiser with the word 'Safari' printed on its side.
However, authorities later said Hanekom had been arrested, not kidnapped, and that he had been facing "a number of charges".
On Sunday, the Department of International Relations and Cooperation (Dirco) said that Hanekom was doing "well in custody".
News24 previously reported that Hanekom and two Tanzanians were arrested on December 31, and were named by Mozambican authorities as allegedly being part of a jihadist group operating in the region.
According to AFP, the group faced charges including murder and crimes against the state.
Allegedly, Hanekom had been responsible for the logistics of the group and was shot while trying to resist arrest in August. Weapons were reportedly found at his home.
His wife repeatedly denied the allegations.
Amanda's sister Andrie previously told Netwerk24 that the family believed that influential people were misusing the Mozambican police, as they wanted to get their hands on Hanekom's beach property in Palma, in the northern province of Cabo Delgado.
Attempts to contact Dirco for comment on Hanekom's death were unsuccessful.