Organised by chamber music organisation Wigmore Hall at London church St James s - the event saw iconic anthems including Zadok the Priest performed in front of a sold-out crowd.
King Charles, 74, who is on a private solo trip to Romania s Transylvanian region, was snapped smiling as he went for a walk in the village of Valea Zalanului.
Charles is taking a break from official engagements in the UK but will begin his trip with a formal bilateral meeting with Romania s President Klaus Iohannis in the capital Bucharest.