A depressed grandmother has been overwhelmed with happiness since receiving a mysterious greeting card from a local woman identified only by her first name.

In addition to the senior suffering from dementia and depression, she is also disabled, according to her granddaughter Melly. Every day without failure, the grandmother sits by the window at her home in Durham, England so she can wave at passerby.

Not much has ever come from the elderly woman's daily routine—until this week when she received an unexpected holiday card in her mailbox.

"To the lady who waves and smiles, with Christmas wishes," read the card. "It's nice to see you smile and wave when I walk past your house. Please accept my small token gift to give you another reason to smile."

The note, which contained a gift card for UK grocery store chain Sainsbury's, was signed only by a woman named Leigh.

Melly later recounted the heartwarming incident on social media so she could wish the mystery woman a Merry Christmas and thank her for the note.

My Nan is disabled & has dementia. She sits in her chair by the window all day, every day - just looking outside & normally feeling lonely as we all work during the day. When we went to see her today, someone had posted this through the letter box 😭 Merry Christmas, Leigh ❤️ pic.twitter.com/lyzqHMr1xd

— Melly (@MellyMaestro) December 22, 2019

My Nan is disabled & has dementia. She sits in her chair by the window all day, every day - just looking outside & normally feeling lonely as we all work during the day. When we went to see her today, someone had posted this through the letter box 😭 Merry Christmas, Leigh ❤️ pic.twitter.com/lyzqHMr1xd

"My Nan is disabled and has dementia," explained Melly in a tweet. "She sits in her chair by the window all day, every day—just looking outside and normally feeling lonely as we all work during the day. When we went to see her today, someone had posted this through the letter box."

Since publishing the story to Twitter earlier this week, it has been shared thousands of times. Not only that, social media users have been flooding Melly's inbox with pictures of their pets since she also mentioned how her grandmother loves animals.

"She's been so depressed recently. I can't put into words how much this has picked her up!" Melly wrote in several followup posts. "She's barely eaten for weeks because she's been so down and I've just made her a sandwich and she's happily chomping away. I could burst.

"Can't wait to tell Nan how many people have wished her well and show her all the gorgeous pups and cats you've shared. We're all buzzing that you've enjoyed Leigh's kindness as much as we have and I hope she gets to find out, too."

Be Sure And Share This Sweet Story Of Kindness With Your Friends On Social Media…