What does la soeur de Valentin est amusant mean?

This sentence is grammatically incorrect in French. It should be:

"La sœur de Valentin est amusante."

This translates to:

"Valentin's sister is funny."

Here's the breakdown:

* La sœur de Valentin: Valentin's sister

* est: is

* amusante: funny (feminine adjective agreeing with "sœur")

The original sentence used the masculine adjective "amusant" which would be correct if referring to a brother, but not a sister.