Shera, a 21-year-old African lion kept at the Smithsonian National Zoo in D.C., has died.

The zoo announced Thursday she was humanely euthanized this week after a decline in mobility from osteoarthritis, a degenerative disease associated with joint pain and bone stiffness.

In a news release, the zoo said staff had become concerned about her ability to safely move in recent weeks as she became weaker.

Shera arrived at the D.C. zoo in 2006 with her sister Nababiep from a private reserve in South Africa, and a young male named Luke. She would later welcome eight cubs over her lifetime with Luke, and become one of the two oldest living lions in Association of Zoos and Aquariums-accredited zoos.

Luke was humanely euthanized at age 17 in October 2022.

Two of Shera and Luke’s male offspring, Shaka and Jumbe, can be seen at the zoo’s Great Cats exhibit.

“The decision to euthanize an animal is never taken lightly and never conducted independently. Multiple teams — including the animal husbandry team and veterinary team — work together to assess the animal’s quality of life,” the zoo said in a release on Tuesday.

Keepers at the zoo had been managing pain level but said they knew her health would continue to deteriorate.

“Geriatric care required considerable time spent managing Shera with extra TLC, and she loved the attention. Shera was adored and will be greatly missed,” Leigh Pitsko, assistant curator of Great Cats, said.