The Australian Transport Safety Bureau says it's "very likely" that a wing fragment found washed up on Reunion Island, in the Indian Ocean, is part of the missing Malaysia Airlines flight MH370.
The debris is being sent to a military base near Toulouse in France which specialises in analysing aviation wreckage.
Reunion is thousands of miles west of the current search area.
But chief commissioner of the ATSB Martin Dolan says they are confident it does relate to MH370:
The flight disappeared en route from Kuala Lumpur to Beijing in 2014.
If confirmed, the discovery could offers hope of an explanation to the families and loved ones of the 239 missing passengers and crew.
Aviation experts say the wing surface - known as a flaperon - may have stayed afloat due to air pockets in its structure and is almost certainly part of a Boeing 777.
But relatives and officials must await the result of tests to confirm whether it belongs to MH370.
The debris arrived in Paris early today and is due to be transferred to a military base near Toulouse which specialises in analysing aviation wreckage.
Experts will attempt to verify the serial number of the wing-flap before conducting further tests to establish why it separated from the rest of the plane.
French TV showed images of the debris bearing the mark "657 BB" - which would match with a code in the Boeing 777 manual for a right-wing flaperon, according to a document posted on aviation websites.
The remains of what could be a suitcase were also found on the same stretch of rocky beach, in the town of Saint Andre.
A Chinese water bottle and an Indonesian cleaning product also washed up on Reunion Island.
The flaperon was discovered by a local gardener, who said he hopes it might help families mourn and restart their lives.
Mr Begue was searching for a stone to grind herbs when he spotted the fragment in the sea.
He told Sky News: "I went to the water's edge to pick up a stone to smash the herbs, and that's where I saw (it). I went down to the water to see if it was plane debris, and I could see that it was by the rounded shape."
MH370 went missing on 8 March, 2014, with 239 people on board, mainly Chinese nationals.
Investigators believe it headed south into the Indian Ocean after disappearing from radar off the coast of Thailand.
Australia has been leading the hunt for the plane, using sonar to trawl a massive expanse of ocean some 1,000 miles off its west coast.
Reunion is about 2,500 miles west of the current search area.
Oceanographers say it is possible that currents could have swept the debris such a distance - though the piece, even if confirmed as part of MH370, is unlikely to help investigators figure out where the plane came down.
Aeronautic experts will study deformation and damage to the debris to determine whether it was part of a plane that exploded in mid-air or came apart on impact with the ocean.
