A Frenchman held hostage by an al Qaeda-linked group in Mali was reportedly freed as part of a prisoner swap with two jailed militants.
Serge Lazarevic was welcomed home on Wednesday by family members and French President Francois Hollande.
Reports say his release was facilitated by a deal that saw at least two militants - including his alleged abductors - freed from a Malian prison.
The French government has repeatedly denied paying ransoms for hostages.
Another Frenchman who was taken hostage along with Mr Lazarevic, Philippe Verdon, was killed by the group, Al-Qaeda in the Islamic Maghreb (AQIM).
'Taken from their cells'
A prison official in the Malian capital Bamako revealed over the weekend that two men had been taken from their cells to the airport, to be flown to Niger, the BBC's Alex Duval Smith reports from the city.
The men were named as Heiba Ag Acherif and Mohammed Ali Ag Wadossene. Both are said to be members of AQIM, and had been jailed for their alleged role in the abduction of Mr Lazarevic.
An association that honours the memory of Ghislaine Dupont, a French journalist killed in Mali last year, also said the two militants had been freed. The association did not say how it had got its information.
Stephane Le Foll, a French cabinet minister who was asked about reports of a prisoner swap, said only that there had been negotiations.
Analysis: Alex Duval Smith, BBC News, in Bamako
Mid-evening on 9 December, an army helicopter from Niger landed in the capital Niamey from northern Mali. On board were Serge Lazarevic and the key player in his release, Nigerien uranium kingpin Mohamed Akotey.
The journey marked the end of long negotiations of which the details remain the subject of speculation but at least two terrorist suspects were released from custody. After his uncle, Tuareg rebel leader Mano Dayak, died in a plane crash in 1995, Mr Akotey shot to prominence as his successor in talks that led to a lasting peace settlement in Niger.
In 2007, as environment minister, he played a key role preventing a Tuareg rebellion by attracting development support for northern regions from French nuclear firm Areva. An Ifogha Tuareg, his tribe straddles the borders of Niger and Mali and has links to key jihadists.
Mr Lazarevic and Mr Verdon were snatched in Mali in November 2011.
French troops found Mr Verdon's body in the mountains of northern Mali in July 2013.
On Wednesday, Mr Lazarevic was flown to a military airport outside Paris from Niger. Mr Hollande said there were now no more French hostages left anywhere in the world.
The French president credited the governments of Mali and Niger for their help in securing Mr Lazarevic's release. Mr Lazarevic also thanked Mr Hollande and the French government for "having done everything to free me".
In his first words on French soil, Mr Lazarevic said how wonderful it was to regain his freedom. "When you're on the verge of death, you think more about life," he said.
President Hollande warned French travellers not to venture into areas where they could risk kidnap.
"It's a dangerous world," he said.
AQIM kidnapped a number of Western hostages before the French military deployed its forces against the group in January 2013.
There were at one point at least 14 French nationals being held by Islamists in West Africa.
Three Western citizens are still believed to be held hostage in Mali. They are Johan Gustaffson from Sweden, Sjaak Rijke from The Netherlands and Stephen Malcom McGowan, who has dual British and South African citizenship.
They were abducted in Timbuktu in November 2011.