The most common and most likely answer to this crossword clue is the 6 plus 6 letter word FATHER FIGURE
I've seen this crossword clue in Financial Times
F
A
T
H
E
R
F
I
G
U
R
E
Buddy explains!
The straight part
We know that "mum’s male friend" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case mum’s male friend = father figure.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.