Clue: Regiment's patron, old and single, in embrace? That is fine (7-2-5)
Answer: COLONEL-IN-CHIEF
Explanation: Definition: Regiment's patron
A charade of COLONELINCH, an envelope ('in') of O ('old') plus LONE ('single') in CLINCH ('embrace'); plus I.E. (*id est*, 'that is') plus F ('fine'). A convoluted wordplay, and not a use of 'patron' that I had come across before.