Credit: Jim WATSON / AFP via Getty Images

(CNN)—A statement released Monday by the communications director for the late U.S. Senator Lindsey Graham (Republican representing South Carolina) revealed that his death resulted from an aortic dissection due to atherosclerosis.

The statement explained that the preliminary findings came from the Office of the Chief Medical Examiner in Washington, DC, and indicated that "the death certificate will remain pending until all toxicological and microscopic tests are completed, at which point it will be updated to correctly determine and classify the cause of death."

Graham passed away earlier Sunday, and a statement on behalf of the late senator's office said the Graham family "appreciates the prayers at this time and asks for privacy during this extremely difficult period."

U.S. President Donald Trump mourned his prominent ally Graham, describing him as "one of the greatest people I have ever known," following the announcement of his death.

Graham was elected to the Senate in 2002 and was seeking a fifth term.

Graham was a critic of Trump during his 2015 Republican presidential campaign, later becoming a close political ally of Trump during his first term.