Clue: Elderly relatives transfixed by Brussels body, one serving Europeans (8)
Answer: GRECIANS
Explanation: Definition: Europeans
An envelope ('transfixed by') of EC (European Commission, 'Brussels body') plus I ('one') in GRANS ('elderly relatives'). 'Serving' seems just to join wordplay to definition (Chambers does give a definition of Grecian as "an Irish labourer recently arrived in England", but it would be a stretch for that to cover 'serving').