The most common and most likely answer to this crossword clue is the 12 letter word METAMORPHOSE
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More clues leading to the result METAMORPHOSE
Buddy explains!

The straight part
We know that "Develop/as in /classical verses" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case develop/as in /classical verses = metamorphose.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 METAMORPHOSE mean?
METAMORPHOSE verb- (of a moth or insect) To undergo metamorphosis.
- (by extension) To undergo some transformation.
- To transform (something) so that it has a completely different appearance.