Bailey spent most of his life in the company of his cousins, Naja and Malika, with staff often finding them all squished together in the same bed in the morning, the zoo said.
He enjoyed playing with Christmas trees every year, but “nothing would beat his love for a cardboard box or to roll around in elephant poo”, it added.
Lions in captivity live to about 15 to 20 years old, with Bailey developing several conditions in his senior years – including mobility issues, a tumour on his leg and signs of reduced kidney function.
Colchester Zoo said Bailey’s habitat would remain empty while it processed the loss of its “beloved friend”.
“We would like to thank everyone for their support during this difficult time,” it added.
“Saying goodbye to one of our friends is never easy and this loss has come at an exceptionally hard time, following the sad news of the passing of our two Patagonian sea lions, Sydney and Milan.”