A photographer, waiting for a glimpse of the Duchess leaving home on her way to hospital for the Royal birth, revealed that he heard someone shouting a name which sounded like "Lupo" and asking the animal to come to heel.
"Soon after a heard a high-pitched scream which sounded like a dog is distress. I presume that was when they were pulling the poor animal out from between the bars of the gate," said photographer Greg Blatchford.
It was not clear whether the Duke and Duchess had taken Lupo to Bucklebury Manor so that he could be looked after by family members while they were away from home during the birth.
A spokesman for the Royal Berkshire Fire and Rescue Service confirmed that the brigade had been called to Bucklebury Manor shortly before 6pm tonight.
"We were called to an animal rescue. The special unit from Reading was despatched along with an appliance from the nearest station, Newbury," said the spokesman.
"Our crew got to the manor but were told as they arrived at the gates that the dog, which had got its head stuck, had been freed just a few moments earlier so their services were not needed.
"The animal rescue unit was stood down before it reached Bucklebury and the appliance returned home."
Lupo was adopted by the Duke and Duchess in January 2012 around the time of Kate's 30th birthday. He was said to be a comfort to her while William was posted overseas last Spring.
- Daily Mail