Two young brothers and their cousin were wandering through a fossil-rich stretch of the North Dakota badlands when they made a discovery that left them “completely speechless”: a T. rex bone poking out of the ground.

The trio announced their discovery publicly Monday at a Zoom news conference as workers at the Denver Museum of Nature & Science prepare to begin chipping the fossil out of its rock cast at a special exhibit called the Teen Rex Prep Lab. The exhibit’s opening on June 21 will coincide with the debut of the film “T.REX,” about the July 2022 find.

It all started when Kaiden Madsen, then 9, joined his cousins, Liam and Jessin Fisher, then 7 and 10, on a hike through a stretch of land owned by the Bureau of Land Management around Marmarth, North Dakota. Hiking is a favorite pastime of the brothers’ father, Sam Fisher.

“You just never know what you are going to find out there. You see all kinds of cool rocks and plants and wildlife,” he said.

Liam Fisher recalled that he and his dad, who accompanied the trio, first spotted the bone of the young carnivore. After its death around 67 million years ago, it was entombed in the Hell Creek Formation, a popular paleontology playground that spans Montana, Wyoming and the Dakotas. The formation has yielded some of the most well-preserved T. rex fossils ever. Among them is Sue, a popular attraction at the Field Museum in Chicago, and Wyrex, a star at the Houston Museum of Natural Science.

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But none of them knew that then. Liam said he thought the bone sticking out of the rock was something he described as “chunk-osaurus” — a made-up name for fragments of fossil too small to be identifiable.

Still, Sam Fisher snapped a picture and shared it with a family friend, Tyler Lyson, the associate curator of vertebrate paleontology at the Denver Museum of Nature & Science.

Initially, Lyson suspected it was a relatively common duckbill dinosaur. But he organized an excavation that began last summer, adding the boys and a sister, Emalynn Fisher, now 14, to the team.

It didn’t take long to determine they had found something more special. Lyson recalled that he started digging with Jessin where he thought he might find a neck bone.

“Instead of finding a cervical vertebrae, we found the lower jaw with several teeth sticking out of it,” Lyson said. “And it doesn’t get any more diagnostic than that, seeing these giant tyrannosaurus teeth starring back at you.”

A documentary crew with Giant Screen Films was there to capture the discovery.

“It was electric. You got goosebumps,” recalled Dave Clark, who was part of the crew filming the documentary that later was narrated by Jurassic Park actor Sir Sam Neill.

Liam said his friends were dubious. “They did not believe me at all,” he said.

He, Jessin and Kaiden — who the brothers consider to be another sibling — affectionately dubbed the fossil “The Brothers.”

Based on the size of the tibia, experts estimate the dino was 13 to 15 years old when it died and likely weighed around 3,500 pounds (1,587.57 kilograms) — about two-thirds of the size of a full-grown adult.

Ultimately, a Black Hawk helicopter airlifted the plaster-clad mass to a waiting truck to drive it to the Denver museum.

Lyson said more than 100 individual T. rex fossils have been unearthed, but many are fragmentary. It is unclear yet how complete this fossil is. So far, they know they have found a leg, hip, pelvis, a couple of tailbones and a good chunk of the skull, Lyson said.

The public will get to watch crews chip away the rock, which the museum estimates will take about a year.

“We wanted to share the preparation of this fossil with the public because it is a remarkable feeling,” Lyson said.

Jessin, a fan of the Jurassic Park movies and an aspiring paleontologist, has continued looking for fossils, finding a turtle shell just a couple days ago.

For other kids, he had this advice: “Just to put down their electronics and go out hiking.”