The most common and most likely answer to this crossword clue is the 1 plus 7 plus 6 letter word A CERTAIN PERSON
I've seen this crossword clue in Financial Times
A
C
E
R
T
A
I
N
P
E
R
S
O
N
Buddy explains!
The straight part
We know that "He’s no doubt/who we’re talking about" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case he’s no doubt/who we’re talking about = a certain person.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.