Sahee quickly won the hearts of his keepers when he first arrived last year, the zoo says.
"The only difficulty was doing it on a lion, and not your regular moggy," says a vet.
Autopsies show that the lions suffered from dehydration and multiple organ failure.
The 16-year-old, which had fathered three cubs, moved to his Suffolk "retirement home" in October.
Their mum has been "so attentive, making sure her cubs are fed, clean and comfortable", a zoo says.
Clarence and his brother Brutus were rescued from a French circus in 2012.
Keepers say they are "proud that she lived as long as she did" as wild lions only live to about 14.
Amali, 2, developed a life-threatening intestinal obstruction, the safari park in Hythe says.
Wingham Wildlife Park has yet to confirm a date when the public can see view the Asiatic lion brothers.
