The world's most famous sea otter has died after six months of chemotherapy at the Vancouver Aquarium failed to stop his lymphoma.

Twelve-year-old Milo was seen by nearly 17 million people on YouTube when a video surfaced several years ago showing the otter and his late partner, Nyac, holding paws in their tank.

"Milo was the first live sea otter to be diagnosed with lymphoma and the first sea otter treated with chemotherapy in the world," the aquarium stated in a press release. "His response to treatment had been very positive for almost six months. Between intensive treatments, Milo spent time in his sea otter habitat with companion Tanu."

After he was first diagnosed last August, aquarium staff began his treatment in consultation with a team of veterinary specialists from around the world. Their treatment plan will help improve understanding of sea otter diseases and responses to treatment, the aquarium said.

Vancouver Aquarium staff veterinarian Dr. Martin Hau-lena will review the results of Milo's treatment plan over the next few months. He will then share his knowledge with inter-national colleagues, the aquarium said.

Milo was born in Portugal's Lisbon Aquarium on August 14, 1999. He came to the Vancouver Aquarium in September 2000. Milo was predeceased by Nyac, who survived the Exxon Valdez oil spill. She died in 2008 of lymphocytic leukemia.

The average lifespan of sea otters in the wild is 10 to 15 years for males and 15 to 20 years for females. Sea otters in captivity often live longer than their wild counterparts.

During the 1700s and 1800s, sea otters were hunted to extinction along the B.C. coast. Today's B.C. population is descendant from 89 Alaskan sea otters relocated to the west coast of Vancouver Island between 1969 and 1972.