A beloved pair of African lions who lived as companions at the Los Angeles Zoo for the last six years have been euthanized, officials announced Thursday.

The decision to “humanely euthanize” Hubert and Kalisa, the 21-year-old companions, was made by animal care and health staff due to their declining health and age-related illnesses that diminished their quality of life, zoo officials said in a news release.

“In the early mornings, staff would routinely hear Hubert’s waking roars, and I will personally miss hearing them on my walks around the grounds,” said Alisa Behar, curator of mammals at the L.A. Zoo.

Hubert was born Feb. 7, 1999 at the Lincoln Park Zoo in Chicago. Zoo officials said he fathered 10 cubs and met his long-time companion, Kalisa, a female African lion born Dec. 26, 1998, at the Woodland Park Zoo in Washington.

The pair moved to the L.A. Zoo in 2014 but despite their long-time companionship, Hubert and Kalisa never had any cubs of their own.

“You cannot think of Hubert without thinking of his companion, Kalisa; they’ve been an inseparable couple for years,” Behar said.

Officials said the average life expectancy for African lions in the wild is mid-teens and about 17 years in zoos. The African lion is native to the savannas, arid woodlands, and semi-desert regions from south of the Sahara Desert to South Africa.

“Hubert and Kalisa are an iconic part of the L.A. Zoo experience, and our staff and guests have been touched by their loyal companionship,” said Denise Verret, CEO & Zoo Director of the L.A. Zoo. “Their longevity is truly a testament to the level of expert care our veterinary and animal care teams provide for our elderly animals.”