The trip went without a hitch until Teddy, Nicholls and McMahon arrived in Rome.
"But then went to Vatican City where it all went wrong," Nicholls said.
"Jamie was taking a picture of me and Teddy standing outside when one of the Swiss Guards beckoned us over.
"I honestly thought he was going to offer to pose for a photo or to take one of the three of us, but he snatched the teddy bear off me and flung it into a small shed."
The guard spoke no English and Nicholls couldn't get him to return the bear - even with support from bystanders and a translator.
"He just made a sharp hand gesture, saying no."
Nicholls and McMahon had to leave Teddy behind in Vatican City, locked in a dark shed.
On arriving back in New Zealand, Nicholls had to break the news to 18 pupils of Room 2.
"They were really cross and sad. They know they wouldn't steal someone's teddy bear and don't understand why Teddy was taken."
School principal Katheryn Pick said she hoped Teddy would be returned to the school.
"While his adventures make for a funny story, there are 18 sad 6- and 7 year-olds who just want their special bear back."
The children have written letters to the Pope, asking him to intervene and get their bear back for them.
Today, Monsignor Bell said he too was composing a letter to his superiors on the subject.
"I am going to bring it to the Bishop's attention and ask him to inform the Cardinal to see if we can get some movement on this and speed up the process of bringing Teddy home to New Zealand."
He adds he is sure the Swiss Guard involved in Teddy's confiscation meant no harm and the situation is "a simple misunderstanding".