In Denmark they tend to switch the names Christian and Frederik so that a King Christian calls his heir Frederik and he calls his son Christian and so on. For over 500 years they have alternated between King Christian and King Frederik. Margrethe acted as a “Christian” in that her father and son were Frederiks but Frederik has continued the tradition with his son and if Christian’s first child is a boy he’ll likely call him Frederik.
All the more reason to hope for a girl…
House of Brat 