Martin Sheen paid tribute to a 75-year-old Irish nun, Sister Mary Campbell, from Co. Mayo, after she was killed in a road crash in Los Angeles last week.

Campbell, originally from the Kiltimagh area of Co. Mayo, died instantly in the accident in Malibu last Wednesday.

She was a member of the Sisters of St Louis and was based in Our Lady of Malibu.

Cambell was travelling with Co. Longford native Monsignor John Sheridan - who remains in critical but stable condition, when the accident happened.

U.S. ambassador to Malta, Doug Kmeic was driving the car when the accident occurred on Mulholland Drive last week.

Kmeic, 58, is said to have made a full recovery.

Campbell, Sheridan and Kmeic were returning from a function to celebrate the 60th anniversary of the St. Louis order in the U.S.

Police said the accident remains under investigation and that “dashboard control adjustment” may be a factor in the collision.

Sheen and his actor son, Emilio Estevez, were one of the first cars on the scene. Sheen is a member of Our Lady of Malibu Catholic Church and knew Cambell.

He is said to speak at Campbell's memorial mass this week.

Speaking to Fox News, Sheen described Campbell as “one of the dearest people that you could ever know”.

He described her loss was “heartbreaking”.

Campbell moved to L.A. in 1966.

She worked in an elementary school before moving to Our Lady of Malibu in 1983.

There she served as a principal and teacher at the church's school before she retired in 2003.

Sister Brid Long, a friend and regional director of Sisters of St. Louis, said in recent years Campbell spent her time caring for Sheridan.

“Wherever he went, she went,” Long said.

“She was very devoted to the much beloved pastor.”

Sister Mary was well-respected and popular in Malibu.

Sister Brid told the Western People she was “a person of great faith who was gentle, joyful and outgoing”.

“She was very artistic," added Long.

“She did a lot of calligraphy. She was a very good teacher. People would describe her as having a happy, public personality and endless energy.”

Martin Sheen, playing the president in "The West Wing"