A 16-year-old Manhattan Beach boy, described by friends as “one of the best,” died two days after hitting his head on a freeway overpass while standing on a double-decker tour bus, authorities said Sunday.

The parents of Mason Zisette, a soon-to-be junior at Mira Costa High School, allowed a line of more than 100 kids to say goodbye to him before they took him off life support Saturday in the hospital, said the mother of one of the teens.

“The loving and giving nature of the parents is pretty strong and amazing,” said the mother, who asked that her name not be used.

Zisette was celebrating a classmate’s birthday with a large group of kids on a Starline Tours sightseeing trip around L.A. when the accident occurred at about 7:45 p.m. Thursday.

The chartered bus was traveling 45 mph on the southbound 405 Freeway approaching the Arbor Vitae Street overpass in Inglewood when the freak accident occurred, according to the California Highway Patrol.

Bowen Boullianne, 17, one of Zisette’s best friends, detailed the horrific scene that unfolded Thursday night.

He said about 40 kids were all standing up on the top of the bus, ducking when they would spot overpasses ahead. “We were not told to sit down at any point,” Boullianne said.

Zisette was standing with a few friends at the front of the bus, where it was a little higher, taking it all in and having a good time, he said.

Everyone else was facing forward and could see the overpasses; Zisette was faced the other way talking with friends. He had his arms in the air as the bus approached an overpass that was lower than the rest.

“He hit his hands first on the overpass and got whiplash from (the impact). It cranked his head back and he hit the top part of the bus, the glass section,” Boullianne said. “He hit the back of his head really hard. He was instantly knocked out.”

The teen said Zisette slithered to the floor, his feet out in front of him.

Boullianne and a few others ran over to him, yelling for others to get out of the way. He carried a limp Zisette downstairs and put him on his lap.

It took several minutes before the bus was stopped and nearly 20 minutes for an ambulance to arrive, he estimated.

“We just assumed he would wake up from being knocked out to terribly broken hands,” he said.

Zisette was taken off of life support Saturday and died at 5:23 p.m.

Boullianne said Zisette was “one of the best kids I’ve ever known.

“He was so happy no matter what he was doing,” he said. “He always knew how to make people smile and he always knew what to say in every situation to make someone laugh. It’s kind of creepy almost. He never ever made people feel bad. He was positive in any situation.”

Boullianne and his best friend would go to the gym every day around 5 p.m. He called Zisette a “gym freak,” who always pushed himself to do better. He also played on the Mira Costa tennis team.

Though he had a lot of friends, Zisette was the closest to his family — father Matthew, mom Amy and three siblings — “such beautiful people,” Boullianne said.

However, Boullianne and others did not have glowing words for the adult chaperones — the parents of the girl having the party, who rented the bus — criticizing them for their lack of supervision and actions following the tragedy.

“These parents were beyond irresponsible,” Boullianne said. “They didn’t know how to handle the situation well. Me being a 17-year-old kid should barely know how to handle the situation. We handled it better than them.”

The mother of one of the teens who went to the hospital to say goodbye to Zisette said the actions of the chaperones after the accident were “horrifying” — no one called any of the parents even as their children were being detained by police, and the chaperones did not reach out in the days since.

“The people who have been suffering the most (the Zisettes) are the most gracious, and (the chaperones) have done nothing,” she said. “This is a freak accident that could have happened to anybody. It’s how you handle it afterward, the example you set for your children.”

CHP is still investigating the details of the accident. Starline Tours could not be reached for comment.

Boullianne said despite the chaperones’ actions and tragic nature of Zisette’s death, he hopes people will focus on who his best friend was — the happy kid who always had a good time.

“We want to remember how he lived,” Boullianne said. “Not how he died.”