Upset solitary supporter of the king (8)

I believe the answer is:

royalist

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

'supporter of the king' is the definition.
'royalist' can be an answer for 'supporter' (I have seen 'Supporter of monarchy ' mean 'royalist' so perhaps 'supporter' could also mean 'royalist'). I am unsure of the 'of the king' bit.

'upset solitary' is the wordplay.
'upset' is an anagram indicator.
'solitary' anagrammed gives 'ROYALIST'.

Can you help me to learn more?

(Other definitions for royalist that I've seen before include "For queen" , "Supporter of monarchy" , "Civil War participant" , "Monarch's supporter" , "opponent of Republicans" .)

I've seen this clue in The Times.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.