Richard Cooke, the professional hunter accused of killing Xanda, also reportedly killed the cubs’ brother in 2015.
Mr Cooke handed Xanda’s electronic collar back to researchers.
Andrew Loveridge, from the Department of Zoology at Oxford University, told The Daily Telegraph: “I fitted it last October. It was monitored almost daily and we were aware that Xanda and his pride was spending a lot of time out of the park in the last six months, but there is not much we can do about that.”
He added: “Richard Cooke is one of the ‘good’ guys. He is ethical and he returned the collar and communicated what had happened.
“His hunt was legal and Xanda was over 6 years old so it is all within the stipulated regulations.”
“Cooke also killed Xanda’s brother in 2015, he was only about four years old then. Xanda is still a young father at 6.2 years old and has several young cubs.
“We can’t believe that now, two 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...?”
The most controversial animal killings
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Cecil was found beheaded and skinned near Hwange National Park in 2015 and authorities said Walter Palmer, a dentist from Minneapolis, paid a $55,000 (£35,000) bribe to wildlife guides to allow him to shoot the lion with a crossbow.
He was forced to abandon his dental practice for weeks amid the outcry over the killing.
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