First squeeze the oranges and the lemon and put the juice together with the melon cut into cubes in a blender, also squeeze the grapefruit and scrape the remaining pulp into the blender with a spoon.
Then turn on the mixer until the whole thing has a good consistency (if necessary, you could also do this with a hand blender). If you want, you can pass the whole thing through a sieve to remove the melon seeds and remaining pulp.
For a refreshing good start to the day, serve with a few fruits of your choice and just enjoy.