The old ruler of Tibet's a refugee (4)
I believe the answer is:
Here is my best explanation:
'the old ruler' is the definition.
'of tibet's a refugee' is the subsidiary indication.
'of' indicates the answer is hidden within the clue.
'tsar' can be found hidden inside 'tibets a refugee'.
(Other definitions for tsar that I've seen before include "Formal rulings on Islamic law; was aft (anag.)", "Tyrant", "Autocrat", "Monarch of old Russia", "Ruler finally executed", "Title given to the kings of Bulgaria", "Russian leader", "One associated with 26 [KREMLIN]", "Word derived from Caesar, used by European rulers since 1547" and "Title of Russian emperor".)