The four are: Henry VIII, Francis I, Charles V, and Suleiman the Magnificent; all born within a single decade.
2015
Compton, Tania edits
1956
Cogley, John
2010
Bryson, Bill
2000
Sanders, Valerie edits
1996
Miller, David Philip and Peter Hanns Reill edit
1988
Gates, Barbara T.
2013
Safran, John
Watson, Peter
1999
Courtois, Stephane and others
Bryson, Bill edits
1977
Goode, John
1881
Brodrick, Hon George C