You were in league with the Prince all along.
4 seconds sound clip from the Cinderella (1950) movie soundboard.
You can hear this line at 00:58:52 in the Blu-ray version of the movie.
Quote context
[...]
- She what? Why, you... You... You traitor!
- Now, Sire. Remember, your blood pressure.
- Treason!
- You were in league with the Prince all along.
- I tried to stop her, but she vanished into thin air.
- All we could find was this glass slipper.
[...]