PHILADELPHIA (CBS) — Gritty recently celebrated his birthday. And now one of his youngest fans who is battling cancer has a birthday wish of his own for Philly’s beloved mascot.

He wrote a letter that’s touched a lot of people online.

Jack Callahan has a lot ahead of him, the biggest of which — in the mind of any 3-year-old — is turning 4.

Jack’s birthday is Oct. 30 but the little guy won’t be able to celebrate at home. His family, from Charlottesville, Virginia, has been housed at the Ronald McDonald House since June while Jack receives treatment at Children’s Hospital of Philadelphia for cancer, which has spread to his lungs.

“He has a tough road ahead, kind of an uphill road but he’s responding well. We’re hopeful and he’s happy. He stays happy no matter what,” Jack’s dad, Mike, said.

That enthusiasm got a boost immediately after arriving in Philadelphia, when Jack spotted something strange and orange.

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“I think Jack just noticed the pictures of the mascot that they had up on the walls and we told him, ‘That’s Gritty,'” Mike said.

Gritty has become a passion for the 3 year old.

“He’s like ‘Mom, look at Gritty’s googly eyes. Aren’t those cool?’ So I think to a lot of people who initially didn’t take to Gritty, Jack immediately did,” Jack’s mother, Emily, said.

And that led him to this: a letter to Gritty, dictated by Jack and written and recorded with the help of mom and dad.

In a way, Jack asked the questions of Gritty that we all want to know.

“Where are you from? What food do you like to eat?” Jack said in the letter.

He also mentioned that he will dress up as Gritty for Halloween and even wants a Gritty birthday cake.

What Jack didn’t ask outright was to meet the Flyers’ mascot in person. But perhaps Gritty will read between the lines.

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I can’t believe how much love and support came from yesterday’s post about Jack’s letter to @grittynhl. Jack’s world has been flipped upside down in inexplicable ways because of cancer. But one thing the last 8 months has reminded us is the generosity and goodness that lives in nearly all people. To everyone who sent a message, commented, or tagged Gritty on social media, thank you so much. We’ve read every comment and will read these to Jack as well. Our hope is that in 10, 15, 25 years from now, Jack will be able to look back and see all the goodness that came from this awful disease and all the love that exists in the world. Special thanks to @grittyphilly for reposting Jack’s letter and giving it the momentum it has received. Here is a photo of Jack from a few weeks ago while he was between cycles and doing one of his favorite things: sitting on his grandpa’s lap and and being a goofy 3 year old. Because while cancer is terrible and scary and sad, Jack likes to do the same things we all want to do: be close with loved ones and laugh.

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Because while he is a happy boy, Jack has some really hard days. But that fourth birthday and the prospect of one day maybe meeting Gritty provides a lot to look forward to.

Jack’s mom and dad say they have heard that something involving Gritty may be in the works. They say, either way, they hope to host a birthday party that includes fellow CHOP patients, and of course, a Gritty cake.

Alexandria Hoff