A trio of male lions died earlier this month after they were poisoned—but they weren’t just any big cats. They were three of the five brothers, known as “the five musketeers,” who starred in the film Vanishing Kings: Lions of the Namib, which aired on the National Geographic Channel earlier this year. The film traced their pride through the Namib Desert in northern Namibia.

Philip Stander, founder of the Desert Lion Conservation project, the organization tracking the lions, found their carcasses on August 10 near the village of Tomakas, according to the Namibian. It’s suspected that this was an act of retaliation by farmers who had laced a donkey carcass with poison after the lions had killed the donkey.

“This is truly a tragedy for Namibia’s lion conservation efforts in a very challenging environment that balances lion and human coexistence,” Stander said in the Namibian report. With no more than 150 lions remaining in the country, the unnatural loss of any of them is cause for concern.

3 more musqueteers are dead.Desert Lion Project states that the problems of human-lion conflict are complex #namibia pic.twitter.com/2NfMPBfYK9 — Desert Lions (@desert_lions) August 12, 2016

The Namibia Ministry of Environment and Tourism has opened an investigation into the case, according to a statement on its Facebook page. The agency “condemns this illegal activity of poisoning the lions and those involved will face the full wrath of the law,” the statements reads.

This isn’t the pride’s first tragedy. A villager shot and killed one of the other brothers in July after an incident at a temporary cattle post, which intensified fears over the remaining brothers’ safety. The famed lions had become popular with tourists and less afraid of people, Stander told the Namibian.

Concern over the lions’ safety prompted a decision by the government to move the lions from the Tomakas area to the Uniab Delta, which was thought to be safer. But then disaster struck. (Also see “Lions, Hyenas Killed With Poisoned Meat”)

“It’s terrible,” says Marjolein Duermeijer, a producer for the film. “We’ve been following the five of them for a long time, and we already lost one, so it was already terrible.”

Namibia’s desert lions, which mostly roam outside protected areas in remote, arid northern Namibia, evolved to survive some of the harshest conditions for animals on Earth. Thick coats help them adapt to colder weather, and they can subsist without drinking water, consuming prey such as ostriches and antelopes to hydrate themselves.

Like most of the wild lions in Africa, the desert lions have to contend with threats from farmers trying to protect their cattle from the predators. Stander’s organization has been working to try to help humans and lions coexist peacefully.

In December, Wildlife Watch wrote about the deaths of three members of another famous lion pride, the stars of the BBC series called Big Cat Diaries. Those lions died in Kenya after eating the carcass of a cow that had been laced with poison.

As for the famous lions in Namibia, only one of the brothers is left now. Known as Tullamore (his scientific name is Xpl-93), the lion was moved to the area around the mouth of the Uniab River. But he’s since been tracked heading back in the direction of the Tomakas area, likely to search for his brothers, according to an August 22 Facebook post by the Desert Lion Conservation project.