MARLBORO — It's the mystery of the Big Christmas Tip at a Monmouth County diner.

A man left a $500 tip on a $29 check at the Marlboro Diner on Route 9 in Marlboro on Monday with the message "Merry X-mas" written next to the tip line. Manager Ahmad Hassanein told New Jersey 101.5 the generous tipper is not a regular customer.

The only clues to the generous tipper's identity is what looks like "R" in the signature. Hassanein said the card checked out and the tip is on the level.

The server who discovered the tip on the receipt said she was going to cry, Hassanein said. The server already has the money and is sharing it with the rest of the staff.

"Thank you, thank you for being you, thank you for making everyone’s week, bringing smiles to our faces and appreciating the hard work we all put in to running this diner. We appreciate it more than you know. — this world needs more people like you," the diner wrote on its Facebook page.

The Marlboro Diner is the former Silver Star Diner.

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