Need an imaginative excuse for having different surnames with my brother?

[▐▀▀▼▀▀▌ ►Jay◄ ▐▄▄▲▄▄▌]

So me and one of my mates actually look really similar and we've lied to everyone that we're identical twins but we have different names on facebook and stuff and need a good excuse to tell people. any suggestions. anything from realistic to wild and wacky will do

[pinki]

half siblings or step siblings

[Aaron]

Realistic? Pah. Just tell them you like to live on the edge, and sharing surnames with relatives is too mainstream and you're some form of Neo-hipster that's 100% anti conformist.

[Fro]

Your great grandfather was a great war hero and in honor of his memory, your parent's gave one of you his last name as a tribute

[Superstar]

Your dad beat up your mum, your brother hated him for this so much that as soon as he turned 18 he changed his surname to something else, so as not to be associated with your father.

How's that for wacky?

[CREAM]

Say youre parents wanted Other people to be able to diffrentiate between you as in when letters came etc idk lol so they decided to give you different surnames.
You took on you father and your 'twin' took on your mums (her second name before she was married to your dad)