Ann Eliza Young provides an overview of the Joseph/Fanny Alger relationship.

Ann Eliza Young
3rd Hand

Ann Eliza Webb Young, Wife Number 19; or, The Story of a Life in Bondage, Being a Complete Exposé of Mormonism, and Revealing the Sorrows, Sacrifices, and Sufferings of Women in Polygamy (Hartford, Conn.: Dustin, Gilman, & Co., 1876), 66-67

Dustin, Gilman, and Co.
Fanny Alger, Emma Hale Smith, Ann Eliza Young, Clarissa Hancock Alger, Joseph Smith, Jr., Oliver Cowdery
Reading Public

Mrs. Smith had an adopted daughter, a very pretty, pleasing young girl, about seventeen years old. She was extremely fond of her; no own mother could be more devoted, and their affection for each other was a constant object of remark, so absorbing and genuine did it seem. Consequently it was with a shocked surprise that the people heard that sister Emma had turned Fanny out of the house in the night. . . . By degrees it became whispered about that Joseph’s love for his adopted daughter was by no means a paternal affection, and his wife discovering the fact, at once took measures to place the girl beyond his reach. Angered at finding the two persons whom most she loved playing such a treacherous part towards her, she by no means spared her reproaches, and, finally, the storm became so furious, that Joseph was obliged to send, at midnight, for Oliver Cowdery, his scribe, to come and endeavor to settle matters between them. . . .The scribe was a worthy servant of his master. He was at the time residing with a certain young woman, and at the same time he had a wife living. . . .The worthy couple—the Prophet and his scribe—were sorely perplexed what to do with the girl, since Emma refused decidedly to allow her to remain in her house; but after some consultation, my mother offered to take her until she could be sent to her relatives. Although her parents were living, they considered it the highest honor to have their daughter adopted into the Prophet’s family, and her mother has always claimed that she was sealed to Joseph at that time.

BHR Staff Commentary

It's not clear if "seventeen years old" is meant to be Fanny's age when she began living with the Smiths, when she married Joseph, or when she was kicked out of the house.

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