CUPERTINO — A boy riding a bicycle was fatally struck by a big rig Monday morning, according to the Santa Clara County Sheriff’s Office.

The boy was a 15-year-old Monta Vista High School student, according to Councilman Barry Chang, citing information he received from the sheriff’s office.

The student was riding westbound on McClellan Road at Bubb Road at about 8 a.m. when he was hit by the big rig, the sheriff’s office said. He died at the scene, but his identity has not been released.

Officials say the bicyclist was wearing a helmet and backpack.

Sheriff’s Sgt. Kurtis Stenderup said the truck driver turned right on Bubb after hitting the bicyclist and was half a mile away when witnesses caught up with him.

“He was shocked that he was involved in an accident,” Stenderup said. “When he learned of that, he’s been very cooperative.”

Stenderup said the bicyclist was riding in the bike lane. Investigators don’t know what happened, he said.

McClellan between Bubb to Stelling Road was closed for several hours, reopening around 4 p.m.

Staff writer Katie Nelson contributed to this report. Contact Mark Gomez at 408-920-5869. Follow him at Twitter.com/markmgomez.