The US and Russia have exchanged jailed US basketball star Brittney Griner for notorious arms dealer Viktor Bout, held in an American prison for 12 years.
President Joe Biden said Griner was safe and on a plane home from the United Arab Emirates.
"I'm glad to say Brittney's in good spirits... she needs time and space to recover," he said at the White House.
Griner was arrested at a Moscow airport in February for possessing cannabis oil and last month sent to a penal colony.
The Biden administration proposed a prisoner exchange in July, aware Moscow had long sought Bout's release.
The elaborate swap involved two private planes bringing the pair to Abu Dhabi airport from Moscow and Washington respectively, and then flying them home.
According to Politico website they walked past each other on the airport tarmac.
"The Russian citizen has been returned to his homeland," the Russian foreign ministry said in a statement. Hours later he spoke to his family and said he was back on Russian soil. Reports said his plane had stopped for refuelling in the Dagestan region, three hours' flight from Moscow.
Speaking in the Oval Office, Brittney Griner's wife Cherelle praised the efforts of the Biden administration in securing her release: "I'm just standing here overwhelmed with emotions."
When negotiations began to secure Griner's release during the summer, the US made clear it wanted ex-marine Paul Whelan to be included in an exchange.
But it became clear Whelan, jailed in 2018 on suspicion of spying, would not be part of the Russian swap, dashing his family's hopes.
Bout's lawyer, Alexei Tarasov, told Russian TV that from the start the US wanted two of its citizens returned, and Russia's foreign ministry complained that "Washington categorically refused to engage in dialogue".
Paul Whelan told CNN he was "greatly disappointed" more had not been done to free him, as he had carried out no crime: "I don't understand why I'm still sitting here," he said.
President Biden finally signed the order for Bout's release, commuting his 25-year jail term, in a direct swap for Griner.
"In the end, as we have seen, the exchange took place in the format of one for one. Because really an exchange should be equal," said Mr Tarasov.
Bout's wife Alla told Russian TV she had spoken to him only two days ago: "He was supposed to call me tonight. Now we'll see each other and hug each other. That's better than any phone call."
Viktor Bout sold arms to warlords and rogue governments, becoming one of the world's most wanted men.
Dubbed the "merchant of death" for gun-running in the years after the fall of the Soviet Union, the Russian's exploits inspired the 2005 Hollywood film Lord of War, which was loosely based on his life.
- Speaking in the Oval Office, Brittney Griner's wife Cherelle praised the efforts of the Biden administration in securing her release: "I'm just standing here overwhelmed with emotions."