Peel the grapefruit so that the white skin is completely removed. Remove the fillets with a sharp knife between the parting skins. Squeeze the juice out of the parting skins and collect it. Cut the slices smaller as desired. Wash mint, shake dry, cut smaller if necessary
Mix grapefruit juice, sugar, mango, orange and lemon juice in a bowl until the sugar is dissolved. Add the grapefruit slices and mint and chill until serving. To serve, pour into a serving dish and pour on the champagne