Long Islander Jordan Matalon, age 9, was shocked when he walked into a rehearsal for April 11’s Garden of Dreams Talent Show at Radio City Music Hall and standing there was singer-songwriter Shawn Mendes, whose song “Stitches” Jordan will be performing in the show.

“I was like, ‘Shawn Mendes? No way!’ ” the fourth-grader says. “Oh. My. God. It was nuts.”

Jordan performed Mendes’ song for him at the rehearsal. “It was really exciting. He said I did a really good job,” Jordan says.

The Garden of Dreams Foundation is a nonprofit charity that works with The Madison Square Garden Company and MSG Networks Inc. to help children facing obstacles. It works with 25 partner organizations throughout the tri-state area — including hospitals, wish organizations and community-based organizations — to reach children who are facing challenges such as homelessness, extreme poverty, illness and foster care. It conducts more than 500 events each year, including the talent show.

Jordan is in the show because at age 3 he was diagnosed with Wilm’s Tumor. The cancer required the removal of a kidney followed by four months of chemotherapy.

Jordan chose the song “Stitches” because he’s had quite a few, he says. “When I was young I had cancer, so I got stitches on my belly,” he says. “There’s also a port, so I got stitches there also.” And that’s not all — he also once got stitches when he injured his eye area on his bed during a pillow fight. So the song seemed appropriate, he says.

The concert is free and open to the public. It starts at 7 p.m. Radio City Music Hall is located at 1260 Ave of the Americas in Manhattan.