A 32-year-old waiter in Dallas had plenty to smile about when a client left him a whopping $500 tip to thank him for his kindness towards her mother.

The client ordered the cheapest thing on the menu - a flavoured water bottle for $0.37. But the bill with the tip written on it left the waiter flabbergasted. A not written on a napkin explained why.

A day earlier Kasey Simmons was shopping at his local grocery store when in the checkout line, he noticed another shopper, an older woman who was clearly despondent. Other shoppers passed right by her. Simmons did not.

He spoke to the woman. She didn't explain why she was sad, but Simmons lifted her spirits and even paid for her groceries.

"It was only $17, but it's not about the money. It's about showing someone you care."

The tip at the restaurant apparently came from the woman's grateful daughter. The note on the napkin described the mother's anguish as she tried to go about her normal activities on what was the third anniversary of her husband's death.

According to CNN, Simmons choked up as he read the message out loud.

"On one of the most depressing days of the year... you made my mother's day wonderful," the note said. "You insisted on paying. Told her she is a very beautiful woman. I have not seen this woman smile this much since dad died."