Prosan

This term was used for the legitimate children of a Rexin who were expected to succeed, barring any unforeseen future event preventing this.
  The children of a Prosan were referred as 'Young Prosan [name]', losing the 'Young' mention once their former Prosan parent was crowned ruler; in that aspect, the title was hereditary. There could be multiple Prosan in a kingdom.
  Any potential legitimate heir was referred by this title, sometimes with a number if there were many children, such as 'Second Prosan'.
  The term itself was gender neutral.
Real-Life Equivalent
Prince
Alternative Name
The Closest of Blood
Etymology
'prope' close (lat) - 'sanguinem' blood (lat)
Type
Royalty, Hereditary
Status
No longer in official use since 341
Form of Address
His Royal Highness / Her Royal Highness ; then Sir / Ma'am
Current Holders
Past Holders
Reports directly to