Well? The most obvious I can think of is Czar Konstantin. What other non-OTL names are the monarchs of various countries likely to get?
Not sure what you mean, but...
for Great Britain:
Victoria reigns as Alexandrine
Edward VII reigns as Albert I or Albert Edward I
George VI reigns as Albert II or Albert Edward II
For Spain:
Juan Carlos reigns as Juan III
Or, are you talking about alternate names they might have been given at birth?