The star passed away at her home in Los Angeles on Saturday (29Sep12) following a battle with cancer.
Mounsey was born in South Africa and began to take ballet classes at the age of seven. She later trained in London and performed with companies around the world, including the famed Ballet Russe de Monte Carlo.
She became a member of the New York City Ballet in 1948 and worked her way up to principal dancer, originating roles for legendary theatre producer Jerome Robbins in the The Cage, Fanfare and The Concert.
She retired from the stage in 1958 and went on to launch the Johannesburg City Ballet in her native South Africa, before returning to the U.S. in the 1960s and settling in Los Angeles, where she also founded the Westside School of Ballet and taught there for four decades.
A statement posted on the school's website reads, "It is with great sadness that Westside Ballet announces the death of Yvonne Mounsey, founder of Westside Ballet. With a ballet career encompassing more than eight decades, she touched the lives of thousands through her dancing, her choreography, her teaching, and the example she set of a life well-lived. We will miss her very much."