Photo by Ann Batdorf, courtesy Smithsonian’s National Zoo

One of the National Zoo’s female lions, Lusaka, died Thursday evening, zoo officials said Friday. In a statement, the Zoo described Lusaka as “elderly,” and noted that her health had been in decline for several months while she recovered from having a large, cancerous tumor removed from her back.

Lusaka had been at the National Zoo since September 2003, after having been rescued from a private breeder. Her exact age is unknown, but veterinarians estimate that she was about 18. The average lifespan of lions range from about 15 to 20 years.