Should i tell my little sister the truth about santa?

Me and my little sister are real close. She's eight, the same age I was when I figured out the truth about Santa on my own. This Morning she asked me, "Is Daddy Santa?" I didn't know how to respond. On one hand I don't want to lie to her, but on the other I don't want her to lose that special sense of anticipation all kids feel at christmas. What should I do?