Fifteen years later the North Koreans contacted him again. This time, it was more urgent. They flew Roux out to Pyongyang in an operation so secret Roux himself was unaware who his patient would be until he met a frail Kim Jong Il lying in a modern intensive care bed flanked by his doctors.
"They were visibly anxious about the situation - maybe that's why they asked for a foreign doctor, since I had no problem asking Kim Jong Il questions, or telling him what to do," said Roux, who also met a young Kim Jong Un, whom he said appeared moved by his father's deteriorating health.
State media acknowledged for the first time last month that Kim Jong Un, who assumed power in North Korea when his father died in 2011, was suffering from "discomfort" due to unspecified health reasons, prompting speculation over what ails him.
North Korea, founded by the young Kim's grandfather when a post-Japanese colonised Korean peninsula was divided into North and South in 1945, is a hereditary dictatorship - making the health of its leaders an especially sensitive subject.
Kim, who is 31 and frequently the centrepiece of the state propaganda machine, has not been photographed by official media since appearing at a concert alongside his wife on Sept. 3. Footage from an event with key officials in July showed him walking with a limp.
The time Roux spent in Pyongyang treating Kim Jong Il gives him a near-unparalleled insight for a Westerner into the medical facilities enjoyed by the isolated country's ruling family.
"The local doctors were quite competent, and during the discussions I had with them, it was exactly as if I was talking to European doctors. They were at the same medical level as I was," he told Reuters by phone from Paris. "They had almost everything. They had very good facilities."
BEER BOTTLES FOR DRIPS
Healthcare is technically free for ordinary North Koreans, but years of failed economic policy and a lack of basic supplies means it is often only those with enough hard cash to buy medicine on the black market who get the care they need.
"Conditions were everywhere pretty simple, even primitive. There were staff but little equipment - we saw beer bottles recycled as drips," said James Hoare, a British diplomat who visited rural North Korean hospitals in the early 2000s.
Recent reports from the country suggest the situation has improved, albeit not by much.
For the leadership, however, no expense is spared.
Kim Jong Il in his later years underwent frequent check-ups at the secretive Ponghwa Clinic in central Pyongyang.
A large modern structure surrounded by thick foliage and equipped with its own helipad, the Ponghwa Clinic underwent massive renovations in the years following Kim Jong Il's stroke, historical satellite imagery shows.
"If Kim Jong Un has been advised that medical necessity prevents him from participating in public events, then he's probably under the care of staff by the Ponghwa Clinic," said Michael Madden, an expert on the North Korean leadership.
Almost invisible from the roads and small canal that run alongside it, the Ponghwa Clinic is off-limits to nearly all but Pyongyang's core elite leadership and their families.
It is also kept under close military guard, and suspected of contributing research to the isolated country's weapons programmes. In 2006, Tokyo police arrested a North Korean for exporting a freeze drier to the clinic, which investigators suspected could be used in the manufacturing of biological weapons.
The Kim family's palaces, sprawling compounds boasting yachts, jet skis and thoroughbred horses, are also equipped with specialised medical centres - and it was at one of these that Kim Jong Il recovered from his stroke.
Curtis Melvin, a researcher at the Johns Hopkins School of Advanced International Studies, said Kim Jong Un may be recuperating at one of those palaces.
"According to imagery released by North Korean media, Kim Jong Un spends a lot of time at the Kangdong and Wonsan family compounds. Each housing complex has suitable medical facilities and would be capable of supporting him," Melvin said.
"YOUNG AND THIN"
Like his late father, Kim makes regular trips across the country with an entourage of doctors and nurses, according to Madden, the North Korean leadership expert.
The trips are closely documented by state media, but in an uncharacteristic break from a barrage of propaganda that documents the farm and factory visits of an energetic young leader, Kim's activities have gone unreported for a month.
This is not the first time Kim Jong Un has been missing from public view. For most of June 2012, six months after coming to power, state media failed to report on or photograph him for 23 days. He resurfaced the next month at a dolphinarium.
The 31-year-old appears to have gained weight in the months following the late 2013 purge and execution of his uncle, Jang Song Thaek, the most recently published photographs show.
Observers speculate Kim's weight and family background may have contributed to his condition, which could be related to his recent awkward gait and limp.
Roux, who says he still does not know why the North Koreans chose him, declined to give details on what procedures he performed on Kim Jong Il or whether he was paid, citing state and medical confidentiality.
But he did note some changes in Kim Jong Un since he met him in 2008.
"When I saw him he was a young man who seemed to have normal emotions concerning his father, who was ill. He seemed to be very anxious about that. He was very discrete, he didn't present himself as being a huge leader," Roux recalled.
"Physically speaking, he didn't look as he does now. He was a young, thin man."