The most common and most likely answer to this crossword clue is the 8 letter word BRUTALLY
I've seen this crossword clue in Financial Times
B
R
U
T
A
L
L
Y
Buddy explains!

The straight part
We know that "cruel aspect" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case cruel aspect = brutally.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 BRUTALLY mean?
BRUTALLY adverb- In a brutal manner; viciously, barbarically.