Millions on bridge to see King? (7)
I believe the answer is:
monarch
'king?' is the definition.
(king is a kind of monarch)
'millions on bridge' is the wordplay.
'millions' becomes 'm' (abbreviation).
'bridge' becomes 'arch' (I've seen this before).
'm'+'on'+'arch'='MONARCH'
'to see' acts as a link.
(Other definitions for monarch that I've seen before include "one over realm?" , "Head of State" , "Eg, king, queen, emperor" , "Butterfly (emperor, say?)" , "Not a subject" .)