A beloved polar bear has died unexpectedly at SeaWorld in San Diego, just weeks after its companion was moved to a zoo.

Szenja was a 21-year-old female. The park says she died Tuesday.

Caregivers said she has had a loss of appetite and energy for about a week.

A necropsy is planned, but the park says it could be several weeks before the cause of her death is known.

Szenja was born at a zoo in Germany in 1995. Two years later, she was brought to SeaWorld when the park opened its Wild Arctic exhibit.

Lion, bear and tiger live together Show all 7 1 /7 Lion, bear and tiger live together Lion, bear and tiger live together Leo, Baloo and Shere Khan - "brothers" since cubs Noah's Ark Animal Sanctuary Lion, bear and tiger live together Leo watching Shere Khan wade through their enclosure's creek Noah's Ark Animal Sanctuary Lion, bear and tiger live together Leo and Shere Khan Noah's Ark Animal Sanctuary Lion, bear and tiger live together The BLT (Leo, Baloo and Shere Khan) while still cubs Noah's Ark Animal Sanctuary Lion, bear and tiger live together Baloo licking Shere Khan's nose Noah's Ark Animal Sanctuary Lion, bear and tiger live together Baloo nuzzling his "brother" Shere Khan Noah's Ark Animal Sanctuary Lion, bear and tiger live together (From left) Shere Khan, Leo and Baloo on the verandah of their enclosure den Noah's Ark Animal Sanctuary

SeaWorld's only other polar bear, a female named Snowflake, was shipped to Pittsburgh zoo at the end of February. The two had been kept in the same enclosure since 1997.

Thousands of people had signed a petition to keep the two together. Tracy Remain, PETA executive vice president, told NBC: "After losing her companion of 20 years when SeaWorld shipped Snowflake to the Pittsburgh Zoo in order to breed more miserable polar bears, Szenja did what anyone would do when they lose all hope, she gave up.

"This should be a wake-up call to SeaWorld: Stop breeding and shipping animals around, close the animal exhibits, and retire the animals to sanctuaries.

"Until it does, this ship will keep sinking."

Polar bears can live about 18 years in the wild and 20 to 30 years or more in captivity.