LOS ANGELES (Reuters) - Aunt Rosemary was not George Clooney's only famous relative. You can add a certain Civil War American president to the Oscar-winning actor's family tree.

Politics has apparently run in the activist actor's blood for centuries, as website Ancestry.com on Thursday revealed that the "Ocean's 11" star is distantly related to President Abraham Lincoln.

According to Ancestry.com, Clooney is the half-first cousin five times removed from Lincoln, the 16th president. The genealogy website breaks down the connection, explaining the "half" means that two of their ancestors were half-siblings - Lincoln's mother Nancy Hanks was the half-sister of Clooney's 4th great-grandmother Mary Ann Sparrow.

Hanks and Sparrow shared the same mother, Lucy Hanks, but had different fathers. Lucy Hanks was Lincoln's maternal grandmother as well as the 5th great-grandmother of Clooney.

Clooney's aunt was singer and actress Rosemary Clooney, who died in 2002.

Clooney, long noted for his political activism, is a major Hollywood backer of President Barack Obama. He hosted a Democratic Party fundraiser at his Los Angeles home in March that raised $15 million.

Lincoln, a Republican, is considered one of the greatest presidents in the history of the United States. He led the country through the Civil War and is credited with the abolition of slavery, which officially became law in 1865 after his assassination.

He is the subject of an upcoming Steven Spielberg film "Lincoln," starring Daniel Day-Lewis in the title role, which is to open in the United States next week.

Ancestry.com is offering free access to more than 20,000 documents showcasing Lincoln's life, his family tree and the most pivotal moments of his presidential career. The details can be found at www.ancestry.com/lincoln.