Crossword Genius

Film star only has to cross river to get to city (4,9)

Ross

I believe the answer is:

burt lancaster

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

'film star only has to cross' is the definition.
I don't know anything about this answer so I can't judge whether this works.

'river to get to city' is the wordplay.
I cannot quite see how this works, but
'river' could be 'r' (abbreviation for river) and 'r' is present in the answer.
'city' could be 'lancaster' (Lancaster is an example) and 'lancaster' is found within the answer.
The remaining letters 'but' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...

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