The most common and most likely answer to this crossword clue is the 8 letter word MARGRAVE
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More clues leading to the result MARGRAVE
Buddy explains!

The straight part
We know that "Noble fellow" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case noble fellow = margrave.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 MARGRAVE mean?
MARGRAVE noun- A feudal era military-administrative officer of comital rank in the Carolingian empire and some successor states, originally in charge of a border area.
- A hereditary ruling prince in certain feudal states of the Holy Roman Empire and elsewhere; the titular equivalent became known as marquis or marquess.