Welcome, Janetrmi!
Bill Gresham got married for the first time in 1935, separated in 1936, and divorced in 1942. It was the divorce ending the first marriage that Lewis used to rationalize that Gresham's second marriage, to Joy Davidman, was invalid. It had nothing to do with the nature of the first marriage. His thinking was that because the first marriage ended in divorce, the second marriage wasn't a Christian one, so that the Church of England shouldn't consider her a divorcee. The Bishop of Oxford didn't buy Lewis' reasoning, so denied permission for a church sanctioned marriage between Joy and Jack. I'm not aware of what the first wife's name was. Lyle Dorsett, in his biography of Joy Lewis, And God Came In, describes her this way: "...Bill married a New York woman wealthy in her own right..."
