Feel intense sorrow that sovereign tragically can't have son (6)

I believe the answer is:

grieve

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'feel intense sorrow' is the definition.
(I've seen this before)

I cannot understand how the rest of the clue works.

(Other definitions for grieve that I've seen before include "Suffer intense sorrow" , "Suffer great sorrow" , "Mourn, lament" , "Cause great distress to" , "Feel deep sorrow as for a death" .)

I've seen this clue in The Irish Times.

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