CEO Bo Kjellson of Boras Djurpark Zoo said that the cubs had been killed because they could not be sold or moved and because aggression amongst lions in the zoo had become “too big”.
He warned more of the animals could be killed if they cannot be sent elsewhere or do not settle in to the pride.
Speaking to Swedish broadcaster SVT, Mr Kjellson revealed that the six cubs had been called: “Potter, Weasley, Simba, Rafiki, Nala, Sarabi, Kiara, Kovu and Banzai.
He said: “’I think that they were killed after two years.”
He added: “At that time we had already tried to sell or to relocate them at other zoos for a long time but, unfortunately, there were no zoos that could receive them – and when the aggression became too big in the group we had to remove some animals.
“And it had to be them.”
In 2013, Simba, Rafiki, Nala and Sarabi were killed one year after their birth.
Kiara, Banzi and Kovu were killed in 2015 after they were born in 2014.
Just last year Potter and Weasley were born and they were put to death on Tuesday.
Mr Kjellson explained that when an animal does not “fit in” to the group it is the “natural path” to kill them.
He said: “It’s no secret in any way and we do not try to hide that we’re working this way.”
He said it was possible that more lions faced the same fate: “Now the group works well, but some of them could become surplus animals, and then we will try to move them elsewhere.
“It could be that we have to put them to death,” he said.
Gothenburg University animal researcher Helena Pedersen told STV that it is not unusual for zoos to kill animals if they cannot manage them.
She said: “I think we need to think about why it is important for us to have zoos and if it is worth the price that the animals pay for it.”