Hi there!
Knowledge of Java is not a must. As I see, Kotlin borrowed something from Python and other languages, so you will not feel yourself altogether lost trying to get acquainted with it.
Also Kotlin is not Java 
Many things in it are sensibly different.
The different thing is that learning Kotlin to more advanced, professional scale - this will require some java (perhaps advanced too) for certain. Kotlin is built upon java infrastructure so many java tools (e.g. maven / gradle, certain libraries etc) could be (and perhaps should be) naturally utilized.
You also may find that significant amount of tutorials expect of you some knowledge of java. But I believe you’ll be able to overcome it.