I researched this back a long time ago and decided to let others hear about it too to hear your opinions because wow my mind was blown.

In Goosefeathers Curse two sisters are introduced Daisytoe and Flashnose.

Daisytoe is Goosefeather and Moonflowers mother. Moonflowers kits are Snowfur and Bluestar.

Now let's go back

Flashnose also had a kit named Swiftbreeze. Swiftbreeze was Leopardfoots mother and Leopardfoots kit? Tigerstar.

Now the relations are quite far but that is full proof Bluestar is kin to her killer Tigerstar.

Sorry if I gave a headache there!