The most common and most likely answer to this crossword clue is the 5 letter word MALIK
I've seen this crossword clue in The Guardian
M
A
L
I
K
Buddy explains!
The straight part
We know that "former boy band member" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case former boy band member = malik.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.
What does MALIK mean?
MALIK noun- A tribal chieftain in certain areas of Afghanistan and Pakistan, especially among the Pashtuns.
- An upper-caste landlord in the southern part of Bihar in eastern India.