What a horrible thing to have happen to someone.

In June 1943, while pregnant with her first daughter by her husband Oleg Cassini, Gene contracted German measles during her only appearance at the Hollywood Canteen. Daria was born prematurely in Washington, D.C., weighing only 3 pounds, 2 ounces and requiring a total blood transfusion. Because of Tierney's illness, Daria was also deaf, partially blind with cataracts, and had severe mental retardation. Tierney's grief over the tragedy led to many years of depression and may have begun her bi-polar disorder. Some time after the tragedy surrounding her daughter Daria's birth, Tierney learned from a fan who approached her for an autograph that the woman, then a member of the women's branch of the Marine Corps, had sneaked out of quarantine while sick with German measles to meet Tierney, at her Hollywood Canteen appearance.

In her autobiography, Tierney related that after the woman had recounted her story, she just stared at her silently, then turned and walked away. She wrote, "After that I didn't care whether ever again I was anyone's favorite actress." Biographers have theorized and speculated that Agatha Christie used this real life tragedy as the basis of her plot for The Mirror Crack'd from Side to Side. The incident, as well as the circumstances under which the information is imparted to the actress, is repeated almost verbatim in the story. Tierney's tragedy had been well publicized for years previously. During this time, Howard Hughes, an old friend, saw to it that Daria received the best medical care available, paying for all of her medical expenses. Tierney never forgot Hughes' acts of kindness.

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