How to Make It
To make watermelon juice, blend two cups of cubed watermelon in a blender until smooth. Strain through a fine mesh sieve into a pitcher.
Combine bottle of Rosé, St. Germain, watermelon juice, and zest into a large pitcher, chill until ready to serve. When ready to serve, add bottle of Champagne to the pitcher and stir. Fill highball glasses with ice and pour sangria. Garnish with mint, limes, and watermelon slices.