A tiger at a Cambridgeshire wildlife park required an armed escort when she had "life-saving" surgery to remove a tumour the size of a rugby ball.
Amba was accompanied by police and a firearms team for public safety reasons when she travelled to a veterinary hospital in Cambridge last week.
Shepreth Wildlife Park, based nearby, said the 27 stone (171kg) tigress had recovered well from the operation.
She is now back at the park, where she has lived for 10 years, it said.
Amba showed signs of bloating in early October but the park said it was not initially concerned because the animal is bulk-fed up to 15kg to mimic her natural dietary behaviour.
But after the bloating did not go down, 12-year-old Amba was taken in a specially-built steel crate, with police and the park's own firearms team on standby, for her first ultrasound.
The ultrasound suggested a possible tumour deep in her abdomen.
Jackie Demetriou, lead surgeon for the case, said the main challenges of the treatment were making sure Amba was fully anaesthetised and borrowing special X-ray plates from Addenbrooke's Hospital in Cambridge.
"Pleasingly, after getting this far the surgery itself went very well indeed," she said.
"A tiger's internal anatomy is really the same as a domestic cat's, but bigger.
"At this stage we are cautiously optimistic Amba's surgery has been a success and we are very pleased indeed with her progress.
"Tigers are such magnificent animals and, in light of their endangered nature, operating on Amba was an incredible privilege for all of us and an experience I personally will remember for the rest of my life."
Shepreth animal manager Rebecca Willers said they had been "overwhelmed" by Amba's speedy recovery.
"Though she spent her first 24 hours sleeping and we were all concerned that it was touch and go for a while, we were finally thrilled to see her exploring her outside enclosure again earlier this week, and positively seeking food too," she said.