US Senator Lindsey Graham's preliminary cause of death has been divulged following an investigation by the DC Medical Examiner.

Per a statement issued by Graham's office just before 5:00pm EST on Sunday, 'Aortic Dissection due to Arteriosclerotic Cardiovascular Disease,' was the cause of his 'sudden' passing.

'The death certificate will be PENDING until all the toxicological and microscopic testing are finalized, and at that point the death certificate will be updated to reflect the cause of death and appropriately classify the manner of death,' Graham's spokesperson added in the statement.

Hours earlier, agents from the Federal Bureau of Investigation were spotted at Graham's residence in Washington, DC, following an announcement from Director Kash Patel that his agency was providing all necessary resources for the probe.

The FBI stepped in to 'assist' local authorities in the wake of Lindsey Graham's unexpected death, which added to mounting skepticism earlier on Sunday surrounding the US Senator's sudden passing at 71.  

The office of Graham, who had represented South Carolina since 2002, announced in the early hours of Sunday that the senator had 'passed away from a brief and sudden illness.' 

A 911 call for 'cardiac arrest' was placed from Graham's residence around 8.30pm, but no official cause of death has been confirmed, according to multiple reports. 

FBI Director Kash Patel wrote on X on Sunday morning that the agency was 'assisting local authorities and has made every necessary resource available.'

Graham was a vocal supporter of US involvement in conflicts abroad, including both the Russia-Ukraine war and the Iran clashes.

Federal law enforcement sources later told Fox News that as of Sunday, there was no indication of foul play.

Amidst the July 4th recess break in Washington, DC this past week, Graham travelled to Ukraine, met with President Volodymyr Zelensky, and even visited a drone facility which was later destroyed by the Russians.

Graham has also been targeted by Iranian leaders. An Iranian State TV host noted in a Sunday broadcast that she congratulated 'the Iranian people on the death U.S. Senator Lindsey Graham, who has been sent to hell.'

Political commentators, liberal and conservative alike, have stepped up with their own theories about Graham's cause of death.