Bill's Family

Problem
Bill, in his middle-age, marries a young lady but divorces her soon after.

Bill's son marries the young lady's mother.

What is:
 * $(\text a): \quad$ Bill's relationship with the young lady's mother?


 * $(\text b): \quad$ Bill's relationship with his former wife?

Solution
Bill is simultaneously:


 * $(\text a): \quad$ the father-in-law of his ex-mother-in-law

and:


 * $(\text b): \quad$ the stepgrandfather of his former wife.