Milo, the Vancouver sea otter who gained worldwide fame through YouTube, is undergoing cancer treatment.
More than 16 million people have viewed a video of the male sea otter holding hands with a female otter at the Vancouver Aquarium since it was posted in three years ago.
Staff say that the 12-year-old otter, who was born in Portugal's Lisbon Aquarium, has been diagnosed with lymphoma.
A sudden decrease in mobility last weekend prompted multiple tests on the otter to determine why the otherwise active animal was acting lethargic.
Staff veterinarian Dr. Martin Haulena said biopsies and blood work revealed that the otter is suffering the potentially life-threatening illness.
Milo has started a round of chemotherapy and drug therapy and is already showing some improvement, he added.
The animal's long-term outlook is still unknown, however, because Milo is the first living otter to be treated for the disease.
Nyac, the 20-year-old female sea otter seen in the video with Milo, died of chronic lymphatic leukemia in 2008.
The facility's oldest resident came to the Vancouver Aquarium in 1989, along with eight other otter survivors of the deadly Exxon Valdez oil spill.
