Crossword Genius

The old ruler of Tibet's a refugee (4)

Ross

I believe the answer is:

tsar

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

'the old ruler' is the definition.
(I've seen this before)

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for tsar that I've seen before include "Star for a Russian emperor" , "Russian ruler (S, not Z)" , "Rats (anag)" , "Ruler finally executed" , "Despot" .)

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