Preheat oven to 350*F and spray a bundt cake pan with cooking spray.
Whisk together flour, baking soda, baking powder, and salt.
Cream butter on medium speed with an electric mixer until smooth. Add sugar and mix until fluffy. Next, add lemon extract and grapefruit zest; mix well. With mixer running, add eggs one at a time, mixing well between each.
Add half of flour and all of the grape fruit juice; mix until just combined. Add remaining half of flour and all of the champagne. Mix until ingredients are completely incorporated.
Immediately pour batter into the prepared bundt cake pan and bake for 30 minutes, or until a toothpick inserted into the center of the cake comes out clean.
Let cake cool for 10-15 minutes in the pan and then invert on a wire rack to cool completely.