The brother of Paul Whelan, an ex-U.S. Marine currently being held in Russian prison, said they were told beforehand he would not be included in the swap and were "able to mentally prepare for what is now a public disappointment for us."

"At some level, our family has steeled ourselves for this likelihood," Whelan's brother, David, wrote in a statement. "And I think, as the use of wrongful detentions and hostage diplomacy continues around the globe, it's clear the US government needs to be more assertive. If bad actors like Russia are going to grab innocent Americans, the US needs a swifter, more direct response, and to be prepared in advance."

"In Russia's case, this may mean taking more law-breaking, Kremlin-connected Russians into custody," he added. "It's not like there aren't plenty around the world."

David Whelan also made sure to note he and his family were happy Griner has been released and said he knew the cases "were not intertwined."

"There is no greater success than for a wrongful detainee to be freed and for them to go home," he wrote. "The Biden Administration made the right decision to bring Ms. Griner home, and to make the deal that was possible, rather than waiting for one that wasn't going to happen."

The Whelan family issued a similar statement in April when U.S. citizen Trevor Reed was freed from Russia in a prisoner swap. David Whelan alluded to that in his statement Thursday, saying, "The sentiments I shared in April about Trevor are unchanged: this is the event we wish for so much for our own family. She will be reunited with her family. Brittney is free. And Paul is still a hostage."

-ABC News' Cindy Smith

Brittney Griner's wife, Cherelle Griner, called the past months “one of the darkest moments of my life,” but flashed a large smile on her face knowing “BG” will be home soon.

“Today I'm just standing here overwhelmed with emotions, but the most important emotion that I have right now is just sincere gratitude for President Biden and his entire administration," she said as she stood alongside President Joe Biden and Vice President Kamala Harris.

"It’s a happy day for me and my family," she said.

-ABC News' Justin Gomez

Russian Foreign Minister Sergey Lavrov confirmed that Griner was released and the prisoner exchange was carried out at Abu Dhabi Airport.

"For a long time, the Russian Federation has been negotiating with the United States on the release of V.A. Bout," Lavrov said in a statement. "Washington categorically refused to engage in dialogue on the inclusion of the Russian in the exchange scheme. Nevertheless, the Russian Federation continued to actively work to rescue our compatriot."

"As a result of the efforts made, it was possible to agree with the American side on the organization of the exchange of V.A.Bout for B. Griner," he continued.

The U.S. has said for months it had offered Bout as part of a prisoner swap for Griner and Russian detained ex-Marine Paul Whelan.

Ombudsman of the Russian Federation Tatyana Moskalkova said Putin pardoned Griner before her release in the swap and she and Bout "should not serve the rest of their sentences in their respective countries."

-ABC News' Tanya Stukalova

Griner has been swapped for the convicted Russian arms dealer Viktor Bout, according to a senior U.S. official.

Bout was arguably the world’s best-known illegal arms trafficker and his capture in 2008 at a hotel in Thailand came at the end of a nearly decadelong hunt by the U.S.

Bout, 55, emerged as a kingpin in the global illegal arms trade during the 1990s, accused of fueling some of the world’s bloodiest conflicts, particularly in Africa. Sourcing weapons from the huge stockpiles of the collapsed Soviet Union, the Russian used a fleet of Soviet-built transport aircraft to supply vast quantities of arm, often circumventing international embargoes.

Read more about Bout's history, here.

-ABC News' Patrick Reevell