A 9-year-old California boy recently died from a virus associated with the common cold — an extremely rare occurrence that has perplexed his doctors and family, according to a new report.

Soon-to-be fourth-grader Tristan Ang, of Milpitas, fell ill last month and there was initially no cause for alarm, the San Francisco Chronicle reported.

But his symptoms soon worsened, leaving him confused, forgetful and with a bad headache, according to the report. He died on June 28.

“I don’t know why this happened to him,” Mark Ang, Tristan’s father, told the paper. “It was just this freak accident. It could be that God really wanted him up there.”

Tristan had tested positive for adenovirus — most often associated with the common cold — just before his death, according to the report. Adenovirus is a family of viruses made up of more than 50 strains and it wasn’t clear which strain he was infected with, the outlet reported.

Adenoviruses most often cause sore throats, runny noses and coughs and they are thought to cause up to 10 percent of colds. They are also known to cause conjunctivitis, or pink eye, and some strains can lead to diarrhea, according to the report.

Nearly all children have been infected with at least one strain of the virus by the time they reach Tristan’s age — and once infected, a person will become immune to that particular strain, the outlet reported. But since there are so many strains, people can become infected multiple times.

More severe illnesses, including pneumonia — and in rare cases, meningitis or encephalitis — infections in the brain or spinal cord, can also develop from certain strains. But nearly all fatal cases occur in those with weakened immune systems, such as organ transplant recipients.

Even then, death is out of the ordinary, according to the report.

“These are normal childhood infections — it’s almost shocking when you see somebody die from this,” Dr. Yvonne Maldonado, chief of pediatric infectious diseases at Stanford Health Care, told the San Francisco Chronicle. She was unfamiliar with Tristan’s case.

Last year, 11 children died of advenovirus at a New Jersey rehabilitation center. All had extremely fragile immune systems.