Series covering last British king's mortification (7)
I believe the answer is:
chagrin
'mortification' is the definition.
(synonyms)
'series covering last british king's' is the wordplay.
'series' becomes 'chain' (chain is a kind of series).
'covering' indicates putting letters inside.
'last british king's' becomes 'gr' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'chain' going around 'gr' is 'CHAGRIN'.
Can you help me to learn more?
(Other definitions for chagrin that I've seen before include "irritation?" , "anything but delight" , "Annoyance at having been humiliated" , "Feeling of annoyance and embarrassment" , "Strong feeling of embarrassment" .)