The old ruler of Tibet's a refugee (4)
I believe the answer is:
tsar
'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" .)