If not for a stranger halfway around the world, 8-year-old Grant Berg wouldn't be alive today, his mother said.Grant needed a bone marrow transplant , but after an international search, it was an 18-year-old German college student who came to his rescue in 2011, Grant's mother, Kristi Berg told ABC News. And on Sunday night, Grant and his hero met for the first time at the Los Angeles International Airport."I've imagined it so often in my mind and now it is reality," Grant's bone marrow donor, Marvin Zumkley, 22, told KABC-TV, ABC's Los Angeles station. "It was crazy. It was overwhelming, and it was just a good feeling."A year and a half before the transplant, Grant was diagnosed with aplastic anemia , a rare but serious condition in which the bone marrow stops producing new blood cells, Berg said. This includes red blood cells, which carry oxygen; white blood cells, which fight off infection; and platelets, which mend blood vessels and stop bleeding, according to Dr. Hillard Lazarus, who directs UH Case Medical Center's novel cell therapy program in Cleveland but has not met or treated Grant."You need to treat this thing," Lazarus said, adding that it's often unclear what causes aplastic anemia. But only about 600 to 900 people are diagnosed with it every year.Berg said Grant was getting different kinds of transfusions every week for a year and a half before the transplant."For a year and a half, he lived off other people's blood," Berg said. "I can't even count the amount of transfusions he had."And then Zumkley's bone marrow changed Grant's life, she said. "It means everything to me," she added.Grant was also born with only part of his cerebellum, so he'll be tested later this year for genetic conditions, she said.After staying up well past his bedtime to meet Zumkley, Grant fell asleep in the car on the ride home to Temecula, California, Berg said. The plan is for Zumkley to relax for a few days, visit Disneyland and find other ways to enjoy southern California and get to know Grant, she said.