The most common and most likely answer to this crossword clue is the 10 letter word CODE-NAMED
I've seen this crossword clue in The Guardian
C
O
D
E
-
N
A
M
E
D
Buddy explains!
The straight part
We know that "Secretly entitled" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case secretly entitled = code-named.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.