Should I start calling transgendered brother my sister?

I am 15m. My brother (17m), just revealed to my parents and I that he wants to be a girl. When he is 18, he wants to undergo sexual reassignment surgery. My parents are supportive. My mom even put him on hormones to give him more feminine features and to suppress his masculine features.

I’m proud of him too. He shouldn’t be ashamed of this lifestyle choice.

That said, do you suppose it would offend him if I started using “she” and “her” when referring to him. And do you think he would like if I called him my “sister” from now on?

Just curious.

Updates
7 mo
I just asked my brother if I could start referring to her as my sister. Thanks for the advice. I was just a little nervous.

I’m super excited because I now have an older sister! 😃
Updates
7 mo
I seriously wasn’t trying to confuse any body. I was just asking.

Now that Jennifer wants to be acknowledged as a girl, (she was originally my brother Jacob), I will recognize her as a girl. Just double checking to make sure I am doing the right thing.

I love my sister and I don’t want to hurt her!

Sorry if my question was offensive
Should I start calling transgendered brother my sister?
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