Newel K. Whitney died at age 55.  He appears to have had at least 8 wives at his death.,

Whitney’s second polygamist wife, Olive Maria Bishop, allegedly claimed in a deathbed statement that her husband (Newell K. Whitney) died by poisoning at the hands of his first wife Elizabeth Ann. Footnote 41 on page 59 of The Spalding Engima by Cowdrey et al. (2018), citing Arthur B. Deming’s book Naked Truths about Mormonism (1888), p. 22.

Samuel F. Whitney to Arthur Deming:  

I was informed by a creditable party while last in Salt Lake City that Bishop N. K. Whitney’s second wife confessed on her death bed to Bishop Tuttle, of the Episcopal Church, that Bishop Whitney’s first wife gave him poison in a whisky sling she made for him. The first time it made him very sick and the next evening she gave him another, which caused his death. She made three each time, for herself and the second wife without poison.