Unfilial princess prodded by a US leader once (6)
I believe the answer is:
reagan
'a us leader once' is the definition.
I can't judge whether this definition defines the answer.
'unfilial princess prodded by' is the wordplay.
'unfilial' becomes 'a' (I can't explain this - if you can you should give a lot more credence to this answer).
'princess' becomes 'regan' (character in King Lear).
'prodded by' indicates putting letters inside (prod can mean to poke a hole into something).
'a' inserted within 'regan' is 'REAGAN'.
Can you help me to learn more?
(Other definitions for reagan that I've seen before include "US president nineteen eighty one to ninteen eighty nine" , "40th US president, Ronald" , "US president lived in a strange RNA age" , "Former US president" , "Ronald . . . . . ., 40th president of USA" .)