French troops were shocked to discover not only two hostages inside their kidnapper's lair, but another two foreign women whom no one knew had been kidnapped.
In the early hours of Friday morning, French commanders launched an operation to rescue two French tourists held captive in the region of Burkina Faso.
Tracking the kidnappers to a remote shelter, French troops moved in.
Despite careful planning and American and Burkina support, "no one had any knowledge" of the presence of an American and a South Korean, French Defence Minister Florence Parly said at a news conference.
Four "terrorists" also were killed during the pre-dawn operation.
Contacts with the United States and South Korea "show that these countries were probably not aware of the presence of their two nationals on Burkina Faso territory," she added.
French President Emmanuel Macron was on hand to welcome home the French citizens and the South Korean citizen at a military airport outside Paris just one day after the military operation that freed them.
The American woman was expected to be repatriated separately.
Both hostages, Frenchmen music teachers Laurent Lassimouillas and Patrick Picque, disappeared 11 days ago while on safari in the remote Pendjari National Park in northern Benin.
Their disappearance became apparent when they failed to return from sightseeing.
The disfigured body of their tour guide was later found, along with their abandoned vehicle.
Little is known about the South Korean and American hostages, who had apparently been in the kidnappers' hands for 28 days.
Two French special forces officers, Cedric de Pierrepont and Alain Bertoncello, tragically lost their lives during the rescue mission.
In a statement on Friday, Macron expressed condolences over the deaths of the two Marines participating in France's Barkhane Operation, which has been working to root out terrorists roaming the Sahel region.
The two soldiers were reportedly killed at close quarters as they entered one of the kidnappers' four shelters.
In a statement obtained by the BBC, Macron said he "bows with emotion and solemnity before the sacrifice of our two soldiers who gave their lives to save those of our citizens".
A military ceremony for the commanders is planned for next week.
Macron thanked authorities in Burkina Faso and Benin for their co-operation and promised them support in fighting terrorism.
Four kidnappers were also killed during the operation, while two others escaped.
Parly said the kidnappers' identity was not yet known but there were two main militant groups operating near where the French tourists were taken, one linked to al-Qaeda and the other to the Islamic State group.
Army Chief of Staff General Francois Lecointre said the hostages and their captors were in transit in Burkina Faso "with the intention of the kidnappers to take them to Mali."
"Once the hostages were in their hands it would have been impossible to rescue them," the General told reporters.
Islamic extremists have become increasingly active in Burkina Faso, raising worries the militants could be infiltrating northern Benin and neighbouring Togo as well.
France has 4500 troops in a military force in the Sahel aimed at helping local governments fight Islamic extremists.