This publication alludes to one of the few documented experiments that involved coffee, a king, twins, and death:
“Coffee drinking was compared with tea drinking in monozygotic twins in 18th century,” Lars Breimer, BMJ, vol. 312, June 15, 1996, p. 1539. The author, at the Royal Free Hospital School of Medicine in London, explains:
“One of the more peculiar attempts to throw light on the question of whether drinking coffee is bad for one’s health’ was carried out in the 18th century by King Gustaf III of Sweden…. A pair of monozygotic twins had been sentenced to death for murder. Gustaf III commuted their death sentences to life imprisonment on the condition that one twin drank a large bowl of tea three times a day and that the other twin drank coffee. The twin who drank tea died first, aged 83-a remarkable age for the time. Thus the case was settled: coffee was the less dangerous of the two beverages. The king, on the other hand, was murdered at a masked ball in 1792 at the age of 45 and became the subject of an opera by Verdi.”
Here’s video of part of a performance of that opera: