Since there has been no breach of marriage law, how can you explain such a relationship?

Question

Carl Jones introduced Roger Smith to his friend as his Uncle Roger. Roger Smith introduced Carl Jones to his friend as his Uncle Carl.
"If you are uncles to each other," queried one of the friends, "you must also be nephews to each other."
"That's correct," replied Carl.
Since there has been no breach of marriage law, how can you explain such a relationship?

Answer 1

Suppose a divorced or widowed woman A has a son C & woman B has a son D...
A marries D and B marries C and both couples have a son. A&D has a son named Carl Jones and B&C has a sone named Roger Smith.
Now, Carl Jones is step brother of C (being sons of A) and Roger Smith is step brother of D (being sons of B)... So, Carl Jones is uncle of Roger Smith being brother of his father C and Roger is uncle of Carl being brother of his father D and they both are nephews to each other too.

Answer 2

There could be two possibilities, one of them is:
Roger Smith is Carl Jones's Uncle and Carl Jones got married to Roger' aunt (Who is widow or divorced of Roger's Uncle, so there is no breach of marriage law). So, now Carl is Roger's Uncle.