The son of Cecil the Lion, Xanda, is believed to have been shot by a professional hunter in Zimbabwe's Hwange National Park.
The park shared a Facebook post that said the lion had been killed on a hunt by the man who also killed Xanda's brother in 2015.
In the post, the park said six-year-old Xanda, who had several young cubs, was killed on a trophy hunt a few days ago by Zimbabwe professional hunter Richard Cooke.
It added: "We can't believe that now, 2 years since Cecil was killed, that his oldest Cub #Xanda has met the same fate.
"When will the Lions of Hwange National Park be left to live out their years as wild born free lions should...?"
Xanda's father Cecil, a famous and much-loved lion in the park, was killed in 2015 by Walter Palmer, an American dentist.
Mr Palmer said his hunt was legal having obtained all the proper permits, but he faced worldwide condemnation and vandals even targeted his home.
The 13-year-old lion was decapitated and skinned when he was killed two years ago.
Mr Palmer later said he regretted his actions and had not realised the animal was so revered.
He said: "I had no idea that the lion I took was a known, local favorite, was collared and part of a study until the end of the hunt.
"I relied on the expertise of my local professional guides to ensure a legal hunt.
"Again, I deeply regret that my pursuit of an activity I love and practice responsibly and legally resulted in the taking of this lion."
The dentist did not face charges because he had all the necessary paperwork.
Zimbabwe's Environment Minister Oppah Muchinguri-Kashiri said: "We approached the police and then the Prosecutor General, and it turned out that Palmer came to Zimbabwe because all the papers were in order."
Mr Palmer is thought to have paid park guides $50,000 to kill Cecil.
To mark two years since Cecil was killed, the Lions of Hwange National Park posted a tribute on Facebook on 1 July that said: "And the fight continues for the plight of lions in Hwange National Park #CecilTheLion."