One’s O so unloved, a Romeo in awful despair, ultimately! (9,5)

I believe the answer is:

universal donor

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'one's o' is the definition.
The definition suggests a singular noun which matches the answer.

'so unloved a romeo in awful despair ultimately' is the wordplay.
'romeo' becomes 'r' (phonetic alphabet: alpha, bravo, charlie etc.).
'awful' is an anagram indicator.
'ultimately' says to take the final letters.
The last letter of 'despair' is 'r'.
'so'+'unloved'+'a'+'r'+'in'='sounlovedarin'
'sounlovedarin' with letters rearranged gives 'universaldono'.
'universaldono'+'r'='UNIVERSAL DONOR'

Can you help me to learn more?

(Another definition for universal donor that I've seen is " Blood group O person".)

I've seen this clue in The Times.

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