Snooty, the oldest known manatee in the world, died Sunday at the South Florida Museum, one day after celebrating his 69th birthday.

The manatee died in a "heartbreaking accident," the South Florida Museum announced on Facebook Sunday afternoon.

"The circumstances are being investigated so we can be sure we know the full details of what happened," museum officials said. "Our current rehab manatees -- Randall, Gale and Baca -- are all fine."

Thousands of people celebrated Snooty's birthday on Saturday, a "family tradition" for the community in Bradenton, The Herald Tribune reported. The celebration for the 1,300-pound manatee included a four-tier fruit cake and thousands of children singing happy birthday to the mammal.

Guiness World Records named Snooty, who was born in Miami, the "oldest manatee in captivity" in August 2014. He was initially named "Baby Snoots" until people began calling him Snooty around his 21st birthday.

Snooty is also the official mascot of Manatee County.