Regius professor
Concise Oxford English Dictionary © 2008 Oxford University Press:
Regius professor /ˈriːdʒɪəs/
▶noun (in the UK) the holder of a university chair founded by a sovereign or filled by Crown appointment.
– origin L. regius ‘royal’, from rex, reg- ‘king’.
'Regius professor' also found in these Oxford entries:

