Brittney Griner penned a letter to supporters on Wednesday, thanking an American imprisoned in Russia for his correspondence during the 10 months she was locked up in a Russian prison and later in a penal colony.

Griner, who was released from Russia earlier this month in a prisoner swap for convicted arms dealer Viktor Bout, posted her letter, which was also addressed to Paul Whelan, on her Instagram page.

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Paul Whelan in 2020

Paul Whelan, a former U.S. Marine who was arrested for alleged spying, listens to the verdict in a courtroom at the Moscow City Court in Moscow June 15, 2020.  (Sofia Sandurskaya, Moscow News Agency photo via AP, File)

"Thanks to the efforts of many, including you, I am home after nearly 10 months. You took time to show me you cared and I want to personally take the time to write you and say that your effort mattered," her letter read. "Your letters helped me to not lose hope during a time where I was full of regret and vulnerable in ways I could have never imagined. Thank you from the bottom of my heart. Because of you I never lost hope.

"Your letters were also bigger than uplifting me. They showed me the power of collective hands. Together, we can do hard things. I’m living proof of that. My family’s whole now, thanks to you. We are fortunate to get to spend the holidays together. However, there remain too many families with loved ones wrongfully detained."

She then asked her fans reading the letter to also write to Whelan.

Brittney Griner walks off a plane after returning to the U.S.

Brittney Griner's reintegration after release from a Russian jail. (U.S. Army South photo - Miguel Negron)

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"Those families stood alongside you and all who supported the WeAreBG campaign, to bring me home and it’s our turn to support them. I hope you’ll join me in writing to Paul Whelan and continuing to advocate for other Americans to be rescued and returned to their families.

"Thank you again from the bottom of my heart. I hope your holiday season is full of joy and love."

Whelan was a Michigan corporate security executive who regularly traveled to Russia. He was arrested in December 2018 while visiting Moscow for a friend’s wedding. He was convicted of espionage charges that he and the U.S. government say are baseless. He is currently serving a 16-year sentence.

Brittney Griner in the WNBA Finals 2021

Phoenix Mercury center Brittney Griner, #42, drives past Chicago Sky forward Candace Parker, #3, during the first half of Game 1 of the WNBA Basketball Finals, Sunday, Oct. 10, 2021, in Phoenix. (AP Photo/Ralph Freso, File)

Upon Griner’s release, President Biden said the U.S. was not giving up on Whelan.

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"For totally illegitimate reasons, Russia is treating Paul’s case differently than Brittney’s, and while we have not succeeded in securing Paul’s release, we are not giving up," Biden said.