The most common and most likely answer to this crossword clue is the 8 letter word CRUZEIRO
I've seen this crossword clue in The Times
C
R
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Z
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More clues leading to the result CRUZEIRO
Buddy explains!
The straight part
We know that "A Brazilian’s real ancestor" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a brazilian’s real ancestor = cruzeiro.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.
Crossword Answer definitions
CRUZEIRO noun- The monetary unit of Brazil from 1942 to 1986 and 1990 to 1993.