Posted on the doors of Market Diner is a letter from a family of longtime regulars. It includes warm memories and features a picture of two children, standing in front of distinctive Art Deco building and beaming at the camera. But the tone of the letter is bittersweet.

"We are saddened that the diner is closing at the end of the month," it began.

The stand-alone diner at the corner of 43rd Street and 11th Avenue will serve its final meal Sunday after 53 years of service. Its closing, first reported on Tuesday by the preservationist Jeremiah Moss in his Vanishing New York blog, comes as a blow but not necessarily a surprise to patrons and staff.

"I suppose it's a sign of the times," said Charles Gomez, 55, a retired television journalist, over a bowl of soup Tuesday. He has been a regular at the diner since 2002.

From the restaurant's high windows, one can glimpse the kind of modern residential building that will occupy the space. Permit filings reported by The Real Deal indicate plans for a 13-story mixed-used building on the property, which was bought by the Moinian Group for $5.9 million in 2004.

The developer didn't immediately respond to a message for comment.

Vasilis Plakias, the manager for the last three years and brother-in-law of one of the current co-owners, said there were hardly any complaints and word-of-mouth made its popularity grow.

"Whoever comes in, even for the first time, they love it here," he said.

Business was great, according to Plakias and he "expected to be doing even better over the next year," had it not been for the development plans. The manager noted the diner has become so popular that TripAdvisor ranked it #98 out of 11,566 NYC restaurants.

Gomez said the staff's enthusiasm was just as impressive as the meals.

"This diner has become an extension of my kitchen," he added. "These people, they're not just servers. They're family."

Were it not for the flat-screen television and other modern amenities, stepping into the diner would be like stepping into another decade. It closed temporarily in 2006 and reopened in 2008 under new ownership. There were some renovations, but it retained the aesthetic of a 1960s century New York diner, with rows of orange booths and a long counters.

On 24-year-old diner yesterday, who only wanted to be identified as Nicholas, who has eaten at Market Diner regularly, said the writing was on the wall when the cranes and modern buildings started popping up around the restaurant.

"I see more of these buildings being put up every year," he said

As Gomez finished his soup at the booth by his window, he reflected on how Market Diner's demise represented another part of a sad trend in New York history.

"We're losing a slice of history with these diners. We're losing the fabric of what made New York New York."