A late 17th century gold, portrait miniature mourning ring for Charles I

A late 17th century gold, portrait miniature mourning ring for Charles I
The oval bezel with painted enamel portrait of Charles I under rock crystal, wearing plain shirt and garter sash, the mount engraved in black enamel foliate decoration, the inside of the hoop engraved with the legend Prepared be to follow me, with crown between the initials 'C R', circa 1680