'Inseparable' elderly lions Hubert and Kalisa are put down together at LA Zoo so that neither has to live alone after age-related illnesses saw the 21-year-old companions suffer 'rapid decline in heath'

• African lions Hubert and Kalisa, 21-year-old companions who were 'inseparable', were put down together at their home in the Los Angeles Zoo, officials said
• Both had far outlived their normal lifespan but had been in 'declining health' while age-related illnesses 'diminished their quality of life', said zoo officials
• The zoo chose to make the 'difficult decision to humanely euthanize' the lions Thursday, said the officials in a statement
• Both were known for their 'undivided attention' on each other as they rested and 'cuddled and nuzzled often', said an animal programs director at the zoo 
• Hubert and Kalisa lived together for six years in Los Angeles after being moved from their previous home at Seattle's Woodland Park Zoo, where the lions met

A pair of 'inseperable' African lions were put down together at their home in the Los Angeles Zoo so neither would have to live alone, officials said.

Hubert and Kalisa were both 21 years old and had far outlived their normal lifespan of 14 to 17 years.

But were in 'declining health', the zoo said, and age-related illnesses had 'diminished their quality of life'.

'The Los Angeles Zoo is sad to announce the death of our African lion pair, Hubert and Kalisa,' zoo officials said in a statement Thursday.  'Animal care and health staff made the difficult decision to humanely euthanize the 21-year-old companions.'

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Hubert and Kalisa, a pair of 21-year-old lions who were 'inseparable', were put down together at their home in the Los Angeles Zoo, officials said

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 Both Hubert and Kalisa had far outlived their normal lifespan, but were in 'declining health', the zoo said. Hubert is pictured lovingly cleaning Kalisa as the two lounged at their home in the zoo

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The couple were in 'declining health', the zoo said, and age-related illnesses had 'diminished their quality of life'

The zoo has no plans to add more lions, for the moment. 

Hubert and Kalisa's pairing started at Seattle's Woodland Park Zoo, where the lions met before being moved to LA in 2014. 

While Hubert fathered 10 cubs, he never had any with Kalisa. Hubert was born Feb. 7, 1999 at the Lincoln Park Zoo, while Kalisa was born Dec. 26, 1998 at Woodland Park. 

'This is a very hard loss for our Zoo community,' said Alisa Behar, curator of mammals at the zoo.  'You cannot think of Hubert without thinking of his companion, Kalisa; they've been an inseparable couple for years.' 

Animal programs director Beth Schaefer told the LA Times that the lions were 'charismatic both together as partners and separately.'

'Their undivided attention was always on the other as they rested together, cuddled and nuzzled often.'

African Lions are expected to live until their mid-teens in the wild, and usually reach age 17 while living in zoos. 

'Their longevity is truly a testament to the level of expert care our veterinary and animal care teams provide for our elderly animals,' said Denise Verret, the zoo's director.

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The union of Kalisa and Hubert (pictured) started at Seattle's Woodland Park Zoo, where the lions met before being moved to LA in 2014

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While Hubert (lying asleep) fathered 10 cubs, he never had any with Kalisa

She described the two lions as having been an 'iconic part of the L.A. Zoo experience', and that staff and visitors were 'touched by their loyal companionship'.

The animals have a declining population of anywhere between 23,000 to 39,000 lions and are listed as 'vulnerable to human-wildlife conflict', by the International Union for Conservation of Nature Red List of Threatened Species. 

Hubert and Kalisa were so close that their union was used to help celebrate Valentine's Day at the zoo. 

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Hubert and Kalisa were so close that their union was used to help celebrate Valentine's Day at the zoo. An image form a short video posted on Facebook is pictured

African lions can sleep as many as 20 hours per day to conserve their energy, according to the zoo's website.

Unlike most cats, the lions are a 'highly social species'. 

They typically live in 'prides, or groups. Prides of lions often include a few males along with several females and their young, the zoo said.