The boyfriend of the U.S.-Russian ballerina who was sentenced Thursday to 12 years in prison after pleading guilty to a treason charge tells Fox News Digital that she should "keep the faith strong" as it’s "just a matter of time" until America gets her back. 

Chris Van Heerden made the remarks as the attorney representing Ksenia Karelina — who was detained in Russia in February over allegations that she donated $51 to a Ukrainian organization that passed the money onto the country's military — is planning to appeal the case. 

When asked by Fox News Digital if he had a message for Karelina following the sentencing Thursday, Van Heerden said "If I could just tell her that she is loved – all over the world, people are fighting for her, we have not forgotten about her. I want to remind her not to lose hope, keep the faith strong because now more than ever, don’t lose hope. Keep your eye on the prize because we will get you back." 

"Stay strong, it’s just a matter of time," he added. 

AMERICAN BALLERINA LEFT OUT OF RUSSIA PRISONER SWAP PLEADS GUILTY TO TREASON: REPORT 

Ksenia Karelina and Chris Van Heerden together

Chris Van Heerden says Ksenia Karelina must "keep the faith strong" despite her sentencing. (Fox News)

Karelina’s attorney Mikhail Mushailov was quoted by the Interfax news agency as saying Thursday that "she admitted guilt in part in transferring the funds, but did not admit her intent to transfer the funds to the organizations where they were most likely received." 

"She did not assume that the funds she transferred would be used for anti-Russian actions," he also said. 

Russia’s Federal Security Service, according to The Associated Press, said Karelina "proactively collected money in the interests of one of the Ukrainian organizations, which was subsequently used to purchase tactical medical supplies, equipment, weapons, and ammunition for the Ukrainian armed forces." 

Karelina, a dual-citizen, lives in Los Angeles but was taken into custody while visiting family in Russia. 

BOYFRIEND OF AMERICAN BALLERINA DETAINED IN RUSSIA SAYS PRISONER EXCHANGE IS ‘ONLY BET’ TO BRING HER HOME 

Ksenia Karelina

Ksenia Karelina is seen in Maryland in December 2015. She has been sentenced to 12 years in prison in Russia after pleading guilty to a treason charge, reports say. (Eleonora Srebroski/Handout/Reuters)

Authorities reportedly have examined Karelina’s phone, producing photos that appear to show her at an anti-Putin and anti-war protest in Los Angeles, where she was holding a sign declaring, "We want peace." 

A State Department spokesperson told Fox News Digital following Karelina’s guilty plea last week that it was aware of reports of the detention and trial of an American citizen in Russia. 

The spokesperson said the State Department has no higher priority than the safety and security of U.S. citizens overseas and that officers seek to provide detained Americans with assistance. 

Chris Van Heerden speaks in interview

Chris Van Heerden tells Fox News Digital that Karelina should know that "we will get you back." (Fox News)

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The spokesperson also reiterated a travel warning from the State Department advising Americans not to travel to Russia, due to the risk of unjust detention. 

Fox News' Taylor Penley and Peter Aitken contributed to this report.