Union with Diana in royal family (6)
I believe the answer is:
tudors
'royal family' is the definition.
(I've seen this before)
'union with diana' is the wordplay.
'union' becomes 'tu' (abbreviation for trade union).
'with' says to put letters next to each other.
'diana' becomes 'dors' (I can't explain this - if you can you should believe this answer much more).
'tu'+'dors'='TUDORS'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for tudors that I've seen before include "English dynasty in the 16th century" , "English royal house" , "Members of a house" , "English monarchs from Henry VII to Elizabeth I" , "Members of English royal line" .)