Popped the question when invited (5)
I believe the answer is:
asked
This clue is a double definition.
'popped the question' is the first definition.
(I've seen this in another clue)
'invited' is the second definition.
(I've seen this in another clue)
'when' acts as a link.
(Other definitions for asked that I've seen before include "Made a request" , "Enquired; invited" , "Questioned" , "Put a question to" , "Inquired" .)