Billy By can’t stand to see his father sad.

But you already knew that. Just about everybody with Twitter, or a TV, or even a pulse knows that. Thanks to a viral tweet sent over the weekend, the world now knows that on the day Billy’s father, Satharith By, first opened his new sunny yellow doughnut shop in Missouri City, hardly anyone showed up to buy his doughnuts, causing a sullen face that nearly broke his son’s heart.

“My dad is sad cause no one is coming to his new doughnut shop,” Billy tweeted, shortly after closing time on Saturday, adding a sobbing emoji and photos of his dad next to still-full cases of doughnuts. He hoped some of his friends would see.

He never expected you’d see it, too — much less that it would be retweeted more than 330,000 times, and land Billy’s Donuts on news segments around the country, including “The Today Show.” He certainly never thought it would lead to lines snaking out the shop door as his parents raced to keep the doughnut displays full.

But in the social media age, the right tweet can change everything.

The rush of retweets began immediately. And by the time Billy went to bed Saturday night, he felt the need to warn his dad.

“Dad, make a lot of doughnuts,” he said.

Satharith smiled. On Saturday, he still didn’t know quite what Twitter was — or Instagram, where the store’s following ballooned from 35 followers to more than 125,000.

He learned pretty quickly. On Sunday morning, the shop sold out — even as Satharith spent the majority of the day making extra batches in the back of the shop. He kneaded and beat the dough, folding it and rolling it out again and again — piling it high and spreading it thin over and over in a rhythmic process, like a never-ending tide of dough sweeping across the baking table he’d spent two weeks making by hand in his garage.

The Bys called in aunts and other family members to help out, as Satharith rolled, cut, glazed and fried. His wife Nakry took orders up front.

“It got crazy,” Nakry said a little after 11 a.m. on Tuesday — normally a quiet time in doughnut land. But there’s no such thing as a quiet time at Billy’s this week. And for Nakry and Satharith, this has been a long time coming.

Satharith came to America in February 1981, as a refugee from Cambodia; Nakry came a month later. He worked as a machinist — hence his deft skill at creating his own tools, like the jumbo-sized metal rolling pin he uses at the new shop. Nakry found a job at Wendy’s, where she was still working when her mother and Satharith’s mother set them up.

They were married in 1983, and saved diligently to open their first doughnut shop in 1993. They named it Billy’s after their son, then a toddler, and became part of Houston’s doughnut shop community, in which roughly 90 percent of stores are owned by Cambodian-Americans.

For 24 years, their shop and their son were the center of the Bys American dream. Then, in 2016, Nakry’s health declined; first came kidney stones, then a cyst. With all the pain, she could no longer bear standing on her feet all day. Satharith couldn’t run the shop alone, and they had to sell the business they’d built from scratch.

“And then I had to stay home, I had nothing to do,” Nakry said on Tuesday, a hint of sweat beading along the brim of her ballcap as she pivoted around the small space behind the counter, from where she keeps the tongs to where she swipes credit cards, attempting to multitask her way through the line. “And we tried to save money to open this one. And then, the first couple days it was so quiet, and I was so sad.”

She obviously wasn’t alone in that feeling.

“I was really so sad,” said Satharith. “It was too slow. And I told my wife maybe we’d have to sell the shop and go out to work. And then Billy was so sad. So he said, ‘I can help you Dad. I’ll make this better.’ And he did.”

Billy's Donuts isn’t the first Houston business to find a second wind thanks to a heartwarming social post from a kid.

In December 2017, Jacqueline Garza sent out an all-caps plea asking people to patronize her father’s Mexican eatery, La Casa Bakery and Restaurant in the Near Northside.

"He been thinking about closing but I can't let that happen, spread the word," Garza tweeted about her father, after a long string of disappointing sales. Twitter rallied. Soon, it had been retweeted more than 60,000 times, and sales quadrupled, saving the bakery from a grim fate.

But Billy’s tweet went even farther. On Monday, a group of Twitter employees who were in Austin for the annual South by Southwest festival hopped into a car and drove to Missouri City to buy out the store’s supply of doughnuts. It was the least they could do, the company said in an email to the Chronicle.

“With just one tweet, Billy sparked an outpouring of love and support around the world,” a spokesperson wrote. “We’re here to show him ours.”

The company has engaged with and amplified stories like Billy’s before. But never to this level. And while Twitter is usually reserved for 280 characters and a brief, 15-minute blip of fame, the eye on Billy's Donuts continues to linger. On Tuesday, Satharith easily made more than 200 dozen doughnuts. That’s less than the previous two days, he said, but still well over what he’d anticipated the demand would be.

“I wasn’t expecting it to be this crazy this early in the morning,” Joe Baltazar of Sugar Land said at around 11:15 a.m. Tuesday, as he waited for his chance to pick up a half-dozen glazed doughnuts and a couple ham-and-cheese croissants.

It’s out of the ordinary for Baltazar to even stop at a doughnut shop. The last time he did was at least six months ago, at a Krispy Kreme in Houston. But he saw the story of Billy and his parents on the news and thought, “I want to support good people like this in our community.”

So he drove out and waited about 20 minutes in line. At one point, he said if they weren’t able to fulfill his order, he’d just come back tomorrow.

“This is family,” Baltazar said “This is local. This is community and this is a happy place. So supporting them? It’s the least I can do.”