The Pretoria Zoo has bid a sad farewell to 26-year-old black rhino Mbani who died on Monday morning.The zoo shared the news in a statement on the National Zoological Garden's Facebook page."Mbani died from an acute case of cholic that struck him down this morning. It did not appear to be a chronic condition," it shared."The zoo's veterinarians were with him at the time of his death and did all they could to assist him".Mbani was born in 1993 and became a resident of the zoo in 1998."At 26 years he will be sorely missed," the zoo said.Visitors also expressed their condolences for Mbani, sharing memories of when he was a calf.One person commented: "We'll miss him. I still remember when he was small playing with a ball and made everyone laugh because he was so cute. RIP, boy, you were just a year older than me, but I will cherish the times I saw you each time when I went there to look at you."Another commended the efforts of the zookeepers: "A loss for the team who were so dedicated to his well-being."According to the World Wildlife Fund, black rhinos are critically endangered due to poaching, with the number of rhinos thought to be between 5 042 and 5 455.