Fetus

When a band or a band member is fetus, it means in its/their young years.

Fan 1: This is a picture of my favourite boyband when they first started.
Fan 2: Oh yeah, so fetus BSB!

showbiz marriage

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!