Ancient god, or Isis, possibly (6)

I believe the answer is:

osiris

I'm a little stuck... Click here to teach me more about this clue!

'ancient god' is the definition.
'Osiris' can be an answer for 'god' (Egyptian god). I am unsure of the 'ancient' bit.

'or isis possibly' is the wordplay.
'possibly' is an anagram indicator.
'or'+'isis'='orisis'
'orisis' is an anagram of 'OSIRIS'.

Can you help me to learn more?

(Other definitions for osiris that I've seen before include "Egyptian god of the underworld" , "dead judge?" , "Egyptian god of the dead" , "one Egyptians worshipped" , "Egyptian god - sis or I (anag)" .)

I've seen this clue in the Evening Standard.

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