The spunky 6-year-old is a budding social media star who has more Facebook followers than most adults and a YouTube channel that's been viewed thousands of times. His enthusiastic supporters even have a special moniker -- his so-called "Zeiniacs."
Fame, however, is far from being Zein's goal. He just wants to beat cancer.
The Rancho Cucamonga boy is battling Stage 4 neuroblastoma, a rare form of cancer that affects only hundreds of children in the United States each year.
His family received the diagnosis on Valentine's Day.
"It doesn't get any gloomier than this," Zein's father, Tamer Youssef, said. "It's devastating. And that devastation is an understatement."
According to Tamer and his wife, Radwa, signs of trouble first showed up in January, when Zein began complaining of leg pains. The couple was only mildly concerned. After all, Zein was taking a rigorous Taekwondo class.
But the aches they initially thought to be muscle soreness persisted and doctors theorized that growing pains were to blame. When Zein's health began to quickly falter, they thought he might have the flu. And then Zein began to fade.
"It's like watching a beautiful rose just kind of diminish, day by day," Tamer said. "Day by day, the life is going out."
Undeterred, Radwa pushed for a tuberculosis test, half-heartedly hoping it would come back positive.
"Because at least if he had TB, we would know and we would get to the bottom of it," she said.
Tests confirmed TB wasn't to blame but the family never expected cancer.
'He lit up like a Christmas Tree'
"They threw everything at us, except the big "C" word," Tamer said.
That changed when an emergency room CT scan highlighted, for the first time, the cancer that was spreading through Zein's body.
"He lit up like a Christmas tree when they ran the ... scans and the MRI," Tamer said. "An unbelievable sight."
A 3-pound malignant mass had developed behind Zein's left lung and stretched into his abdomen, spreading cancer cells throughout his body and into the marrow of his bones.
For the Youssef family, the fight was on.
Tamer and Radwa prepared Zein for the battle as best they could and launched a Facebook page to keep loved ones up to date on the child's progress.
"We were getting bombarded with so many kind people out there who were trying to reach out and send us prayers," Tamer said. "It was kind of weird in the beginning, to be quite honest ... to put this on Facebook," Tamer said.
A friend agreed to moderate the page for the reluctant family but it wasn't long before the ferociously private couple began to get involved.
"I started interacting with the people on the Facebook page and we started feeling comfortable sharing some of Zein's stuff," Radwa said.
'It became part of our lives'
As Zein embarked on a year that would be full of surgeries, chemotherapy and radiation, he and his family, including 5-year-old sister Malak, found inspiration in the Facebook support.
"It became a part of our lives to look forward to who's going to say the next nice comment to pump us up. Who is going to send us the incredible prayer that's going to make us kneel down on the ground and pray to God?" Tamer said.
The posts on Zein's page soon transformed. Prayers and blood drive announcements gave way to costumed family photos and homemade graphics thanking supporters. A few months ago, the family launched a YouTube channel.
The projects keep Zein entertained during his arduous treatments and during a particularly trying time when he was in isolation, Radwa got the idea for a makeshift music video.
"He was not allowed to step out of the room at all. And I wanted to encourage him about doing this and keep him busy," Radwa said. "'What props are we going to use today?' 'What do you want to wear?'"
And which song? Zein chose the motivational "Firework," by Katy Perry.
The video, which took more than a month to shoot, features Zein flanked by doctors nurses, family, and other little patients -- some holding colorful signs of encouragement -- miming the words to the song and dancing against a backdrop of medical equipment and hospital beds.
In one of the more touching scenes, a smiling Radwa mimes the lyrics, "If you only knew what the future holds. After a hurricane, comes a rainbow."
In another clip, Zein sports a cape and is carried horizontally by hospital staff, as if he were flying.
"He loves dancing and he loves music, so this was one of his favorites, for sure," Radwa said.
'We just reached 5,000 followers'
The video, uploaded to Zein's YouTube channel on December 2, has already been viewed more than 2,200 times. And his Facebook page is really taking off.
"I guess it became an inspiration to others," Tamer said. "And one thing led to another, and before you know it--"
"We just reached 5,000 followers," Radwa is quick to interject.
Tamer and Radwa said they show Zein the page every few days. And during a recent visit to Radwa's workplace, the remarkable boy contemplated his budding social media empire.
"One YouTube channel and a lot of videos. And I've got a Facebook page. It's awesome. I have a lot of people on my Facebook page," Zein said. "I love it."
For him, the encouragement will be key as he ventures through as many as eight more months of aggressive treatment at Children's Hospital Los Angeles, where an entire department is dedicated to treating illnesses like Zein's.
If Zein's cancer goes into remission, Radwa said, the chance of relapse is high.
Still, she doesn't miss a beat when she adds with enthusiasm, "There are kids who are survivors."