If you have a juicer yay for you - add blackberries, strawberries, and raspberries to your juicer and juice into a small cup. Pour 1-2 tablespoons of orange juice into your juicer while it’s running after juicing the berries. Juiced berries have a thicker texture so the orange juice helps to push out more of the berry juice. You should end up with 1/4 cup to 1/2 cup of juice.
If you don't have a juicer then do what I do and run your berries through a blender on grind and then strain them using a fine sieve.
Distribute berry juice among 4 glasses, add 1/4 cup of orange juice to each glass, and top with champagne.