POUR half the champagne into ice-filled glass (preferably a chunk of block ice), then the orange juice, orange liqueur and then the rest of the champagne.
As the name suggests, the orange of Grand Marnier heavily influences this drink. Basically a Mimosa or a Buck's Fizz (orange juice and champagne) with added oomph.
The Mimosa was created in 1925 at the Ritz Hotel, Paris. The Grand Mimosa benefits from the addition of a splash of Grand Marnier liqueur.