Shocking news

So Saturday I got some shocking news from my mom; she told my younger sister and I that we have an older sister that we never knew about until now. I was so shocked I didn't believe it at first, but I am happy and excited to meet her one day. This morning I felt a small amount of anger towards my mom for not telling us sooner but that feeling went away. I'm hopeful that we can eventually get to know each other and 'become' sisters.