Historic events in New Mormon History on 12/26
1973: death of Harold B. Lee, LDS church president with shortest tenure up to this time, seventeen months and nineteen days. At age seventy-four Lee is youngest LDS president to die since Joseph Smith, and Lee's presidency remains briefest until 1995.
Source: See
The Mormon Hierarchy - Extensions of Power by D. Michael Quinn
To see the whole database in chronological order,
Click here. Note that I'm not done entering all the information. While most of these facts come from Quinn's book, I'm seeking the primary sources for each, but this will take a long time.