In March of 1861, renowned novelist Anthony Trollope sent the following letter to a Miss Dorothea Sankey. To this day, it's unknown whether he was joking.
It's worth noting that Trollope remained married to the wife in question, Rose Heseltine. In fact, she also outlived him.
(Source: The Letters of Anthony Trollope; Image: Anthony Trollope, via The Guardian.)
March 24. 1861
My dearest Miss Dorothea Sankey
My affectionate & most excellent wife is as you are aware still living—and I am proud to say her health is good. Nevertheless it is always well to take time by the forelock and be prepared for all events. Should anything happen to her, will you supply her place,—as soon as the proper period for decent mourning is over.
Till then I am your devoted Servant