(CNN) Manila Zoo's oldest resident, fondly referred to as Queen Bertha, passed away Friday of natural causes at the age of 65, according to zoo authorities.

Although the exact age of Bertha is difficult to determine in the absence of any paperwork, the zoo claims that she was born in 1952 -- making her the oldest recorded hippo to have ever lived in captivity.

Bertha was present at the zoo when it opened in 1959, six years before former Philippines President Ferdinand Marcos was elected to power in a nationwide election, and a further seven years before Manila played host to the Beatles during the band's 1966 tour of Asia.

For most of her life she was accompanied by Bert, another hippo, who died in 2008.

"When I went inside to see her, trying to feed her, she would often greet me with an open mouth. Hippos are supposed to be the number one killer in Africa, but not Bertha -- she was so gentle," zoo volunteer Jerry Young told CNN.

'Queen Bertha' was a longtime resident of the Manila Zoo.