Slice the grapefruit in quarters, and do the same with the lime and orange. Hand squeeze, or use a juicer. (Fresh squeezed juice tastes better, of course, but if you need to buy juice go ahead.)
In each of two champagne glasses, add juice of 1/2 a grapefruit, 1/4 a lime, and about a tablespoon (or splash) of orange juice.
Pour champagne over the juice until the glass is full.
Garnish with a lime wedge and serve while still chilled.