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The boyfriend of an American ballerina thrown in a Russian jail for allegedly donating money to Ukraine says he believes there's only one way to possibly bring her home.

"I would say your only bet is a prisoner exchange and, trying to get this, in the talks of the list of Americans to release in the prisoner exchange… that's our mindset," professional boxer Chris Van Heerden told "Fox & Friends First" Monday.

Ksenia Karelina remains detained in a jail outside Moscow on suspicion of treason for allegedly donating $51 to a Ukrainian organization that passed the money onto the country's military. 

In a letter penned to Van Heerden recently, the dual U.S.-Russian citizen shed light on the dire conditions inside her cell and the hardships she's facing in detention.

AMERICAN BALLERINA WITH DUAL CITIZENSHIP ARRESTED IN RUSSIA, FACING LIFE IN PRISON FOR DONATING $51 TO UKRAINE

Ksenia Karelina and Chris Van Heerden together

Chris Van Heerden told Fox News about girlfriend Ksenia Karelina's experiences inside a Russian jail. (Fox News)

"One day, she'll wake up and be very hopeful and very positive. Then another day, she just has no hope," Van Heerden said.

"[She thinks] she'll be there for the rest of her life. That's where her head is at."

Karelina shared with her boyfriend a few of her hardships including no warm water, no darkness for sleep, the risk of getting stuck in the cold while on the rooftop, and only showering once weekly.

"She told me she's got a 6 a.m. wake-up call, so she's got to go to bed by 10 p.m. at night," Van Heerden said.

BOYFRIEND OF BALLERINA DETAINED IN RUSSIA SAYS IT ‘MAKES ME HOPEFUL THAT AMERICA IS FIGHTING FOR HER'

Ksenia Karelina

Ksenia Karelina, pictured here in custody, is reported to be a resident of Los Angeles.  (Facebook/RIA Novosti)

"The lights stay on all the time, so she's got trouble sleeping. You get to go out once a day to the roof. Obviously, it's snowing, it's cold, but sometimes you go to the roof, and they lock the door, and you stay up there for hours, so she chose not to go up…"

Karelina, reportedly a resident of Los Angeles, flew to Russia to visit family earlier this year. Reports emerged last month that she was taken into custody for alleged treason.

Van Heerden has since called on the U.S. government to bring her home. 

US MARINE  VETERAN PAUL WHELAN JAILED IN RUSSIA ATTACKED IN PRISON, FAMILY SAYS

"I feel like the more I speak to media now and the story blows up, the more attention will be brought to it and the more attention brought to this will urge the U.S. State Department or whatever needs to be urged to help get Ksenia back," he told Fox News in a previous interview.

"She's an American citizen, and like I said, she's very proud to be Russian, but she's also very proud to be American." 

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Fox News' Greg Norman and William La Jeunesse contributed to this report.