Judy Lewis (1935-2011) was the biological child of Hollywood greats Loretta Young and Clark Gable. She was conceived during filming of the aptly named Call of the Wild. Loretta - who was unmarried 1931-1940 - always passed Judy off as a child she'd supposedly adopted (following a long "illness" by Loretta, in which she'd remained publicly out of view for months) from a California orphanage.

Here's Wikipedia's Judy Lewis article.

Additional details of the story follow, from Wikipedia's Loretta Young article:

Young did not want to damage her career or Gable's. She knew that if Twentieth Century Pictures found out about the pregnancy, they would pressure her to have an abortion....Young, her sisters, and her mother came up with a plan to hide the pregnancy and then pass off the child as adopted. When Young’s pregnancy began to advance, she went on a "vacation" to England. After returning to California, she gave an interview from her bed, covered in blankets; at that time, she stated that her long movie absence was due to a condition she had had since childhood. Young gave birth to a daughter, Judith, on November 6, 1935 in Venice, California....Weeks after her birth, Judith was placed in an orphanage. Judith would spend the next 19 months in various "hideaways and orphanages" before being re-united with her mother; Young then claimed that she had adopted Judith. After Young married Tom Lewis, Judith took Lewis's last name. // Few in Hollywood were fooled by the ruse. Judith (Judy) Lewis bore a strong resemblance to Gable, and her true parentage was widely rumored in entertainment circles. When Lewis was 31 years old, she confronted Young about her parentage; Young privately admitted that she was Lewis's birth mother....Young refused to confirm or comment publicly on the rumors until 1999, when Joan Wester Anderson wrote Young's authorized biography. In interviews with Anderson for the book, Young stated that Lewis was her biological child and the product of a brief affair with Gable. Young would not allow the book to be published until after her death.

I saw Judy in t.v. interviews multiple times years back and found her likeable, intelligent, and well-spoken (not to mention beautiful). It took only a glance, anytime you'd see her, to realize she most unmistakably was Loretta Young's biological child, as the two women looked near identical. Judy also favoured her dad, Clark, though far more so mom Loretta.

Please check out the following list of titles and celebrities I've created TMDb threads for: https://www.themoviedb.org/list/118052