The most common and most likely answer to this crossword clue is the 2 plus 3 letter word IN LAW
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Buddy explains!
The straight part
We know that "relative after marriage" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case relative after marriage = in law.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 IN LAW mean?
IN LAW noun- A relative by marriage (or through affinity). Affinal relative; affine.
- Sometimes specifically a parent-in-law of one's child, for which the dedicated terms co-mother-in-law, co-father-in-law are rare