Sylvia Sessions Lyon is the only one of the eleven wives who was legally married at the time of her conjugal relations with Joseph Smith.1 As discussed in Volume 1, Chapter 13, she separated from her legal husband when he was excommunicated on November 19, 1842. In 1915, Josephine Lyon signed an affidavit relating a conversation with her mother, Sylvia, that had occurred in 1882 during her mother’s final illness:
Just prior to my mother’s death in 1882 she called me to her bedside and told me that her days on earth were about numbered and before she passed away from mortality she desired to tell me something which she had kept as an entire secret from me and from all others but which she now desired to communicate to me. She then told me that I was the daughter of the Prophet Joseph Smith, she having been sealed to the Prophet at the time that her husband Mr. Lyon had was out of fellowship with the Church.2
For more details, see Brian C. Hales (with Don Bradley), Joseph Smith’s Polygamy: History and Theology, 3 vols., Salt Lake City: Greg Kofford Books, 2013.