In a champagne flute, add the freshly squeezed grapefruit juice.
Add the lime juice and triple sec.
Top with champagne and garnish with mint if desired.
Notes
I highly recommend using freshly squeezed grapefruit juice rather than store-bought juice. Packaged juice will work just fine, but the fresh citrus is even more amazing and zesty from fresh fruit!
If using champagne flutes, fill the flute almost halfway. Then add the lime juice and triple sec. Finish making the drink by filling the rest of the flute with champagne.