They wrote: “The decision was discussed extensively with zoo management and our specialist vets.

“It was based on facts, not emotions. Otters are a species that cannot easily, if at all, live solitarily. It results in severe behavioural issues including self mutilation – regardless of what steps are put in place.”

“However, regardless of all this, when a post mortem was conducted on both boys, it was found that Hutch had the early stages of an aggressive form of lymphoma which would have killed him within a matter of weeks.

“Therefore this decision actually spared him any further suffering.

The zoo said Starsky and Hutch would be “hugely missed” by keepers and visitors.

It wrote: “Thank you for all the joy, mischief, and memories, boys. Rest peacefully together.”