The most common and most likely answer to this crossword clue is the 12 letter word ACCOMPLISHED
I've seen this crossword clue in The Sunday Telegraph
A
C
C
O
M
P
L
I
S
H
E
D
Buddy explains!

The straight part
We know that "Did" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case did = accomplished.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 ACCOMPLISHED mean?
ACCOMPLISHED verb- To finish successfully.
- To complete, as time or distance.
- To execute fully; to fulfill; to complete successfully.
- To equip or furnish thoroughly; hence, to complete in acquirements; to render accomplished; to polish.
- To gain; to obtain.
- (Philippine English) to fill out a form
- Completed; effected; established.
- Having many accomplishments, often as a result of study or training.
- Showing skill and artistry.