Should I tell my dying father...?

I'm starting to question myself for what I have done and I have no idea what I should do. My father and I have had a great relationship forever. We were devastated when my mother died of ovarian cancer(RIP Mom). We eventually got over it as a family and my father remarried to my aunt. I didn't like my the idea at first because I wouldn't want to see my father with anyone else besides my mother and the awkwardness of my aunt becoming my new step mom but I saw how happy he was with her so I eventually accepted it and we grew quite close. Things were going great for them and eventually their 3rd anniversary came around. My sister and I hosted a party for them at a local venue to celebrate the occasion. It was late a party and I made the mistake of getting drunk, so did my Aunt and dad. They ended up argueing about paying for the party, which was a gift from me and my sister, and my dad drove away with my aunt still on at the party. I offered to drive her home because I didn't want anything to happen to her. We drove for awhile when all of a sudden my aunt started hitting on me telling me I looked like my father and eventually she made the move on me by pulling me close and kissing me on the mouth. Because I was drunk, I gave in and we eventually had sex. Weeks later my father was diagnosed with lung cancer and just lately the battle he bravely fought against it was declared a losing cause by doctors. He has been given a less than a month to live. Around this time my aunt frantically called me on the phone saying she was pregnant. She also told me that the it was mine because around the time of the pregnancy my father and her did not have sex because they were constantly argueing. She has not told him about any of this, only that she is pregnant. He thinks it is his and he has been talking about how I'm getting a little baby sister. I don't know what to do. My aunt keeps lying to him saying its his. What do I do, do I tell him the truth, do i let him think its his and let him rest easy, what do i tell my family about this, do I abort this incestial child, is their any legal complications with this. Please help me in my desperate situation.