The most common and most likely answer to this crossword clue is the 12 letter word EPISTEMOLOGY
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Buddy explains!

The straight part
We know that "concern of 26" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case concern of 26 = epistemology.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 EPISTEMOLOGY mean?
EPISTEMOLOGY noun- The branch of philosophy dealing with the study of knowledge; theory of knowledge, asking such questions as "What is knowledge?", "How is knowledge acquired?", "What do people know?", "How do we know what we know?".
- A particular theory of knowledge.