It's a tradition going back generations.
4 seconds sound clip from the The Lion King (1994) movie soundboard.
You can hear this line at 00:14:53 in the Blu-ray version of the movie.
Quote context
[...]
- Your parents will be thrilled, what with your being betrothed and all.
- Be-what?
- Betrothed. Intended. Affianced.
- Meaning... One day, you two are going to be married.
- Yuck!
- Eww!
- I can't marry her. She's my friend. Yeah, it'd be so weird.
- Sorry to bust your bubble, but you two turtle doves have no choice.
- It's a tradition going back generations.
- When I'm king, that'll be the first thing to go.
- Well, in that case, you're fired.
- Nice try, but only the king can do that.
[...]