Royal Navy invested in value (6)
I believe the answer is:
prince
'royal' is the definition.
(prince is a kind of royal)
'navy invested in value' is the wordplay.
'navy' becomes 'N' (common abbreviation eg in RN Royal Navy).
'invested in' indicates putting letters inside.
'value' becomes 'price' (price is a kind of value).
'n' placed inside 'price' is 'PRINCE'.
(Other definitions for prince that I've seen before include "King's son" , "Monarch's son" , "Sovereign's son" , "See 1" , "Panto character" .)