Ellis worked as the senior American medical advisor at Baghdad's Camp Cropper, where Hussein was held for eight months until his execution in December 2006, Fox News reports.
During this period, Hussein who went by the code name 'Victor' grew close to his caregiver, who was known to him by the code name 'Alice.'
The report quoted Ellis as saying that when he told Hussein that he had to return to St Louis to see his dying brother, Hussein hugged him and said: "I will be your brother."
For Ellis, the mission caused serious internal conflict.
"I was always conflicted throughout the whole mission. My job was to keep these people alive and healthy so they could be interrogated," he said.
Ellis says that by remaining 'non-judgmental,' he was able to see another side of a human who was considered to be a brutal killer.
"By me spending time with him, I got to see his other side, a side that you don't hear about. They play by a different set of rules over there," he added.