The most common and most likely answer to this crossword clue is the 4 plus 5 plus 3 plus 6 letter word JUST ROUND THE CORNER
I've seen this crossword clue in The Times
J
U
S
T
R
O
U
N
D
T
H
E
C
O
R
N
E
R
Buddy explains!
The straight part
We know that "coming up" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case coming up = just round the corner.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.