A true story that I never tire to read, by Liselotte, who reports that Philippe sometimes needed her to decypher what he wrote. Here is the exact quote from one of Liselotte's letters:

His writing was so terrible that he often brought for me to read the letters that he himself wrote, and he'd say, laughing: "You are, Madame, used to my writing; take a look at this, I don't know what I wrote. We often laughed about this.

And we can confirm that it's terrible, indeed, with the examples below the cut:

Le Chevalier: And the time his horse threw him into a pond, at Saint-Cloud, do you remember?

Liselotte: How could I forget? He looked miserable, poor thing!

Louis: Is everything all right, brother?