Showbiz marriage is when two celebrities who are in the same band or cast show a deeper relationship with each other over a longer period of time, like a marriage regardless of both people's actual relationship status. The couple in question is often also referred to as an OTP.
Fan 1: Paul McCartney x John Lennon is my favourite famous couple.
Fan 2: I know, it's like a showbiz marriage!
Nephew-in-law (only spouse's nephew).
My nephew-by-marriage is a good person.
My granduncle-by-marriage-in-law is a good person.
Uncle-in-law (only pibling's husband).
My uncle-by-marriage is a good person.
My great-grandniece-by-marriage is a good person.