[JesseK]

I would caution against making it a complete surprise. To get the details of the submission correct, you'll more than likely need to ask the mentor questions rather than go off of heresay or a misinterpretation of something the mentor says in an unrelated context. This is particularly important if your submission will become public or be read by the company the mentor works for. It's also important so the essay itself is clear and more concise.