Mr Bateman learned to fly at the Hawke's Bay and East Coast Aero Club.
Hastings Boys' High School old boy Trevor Morley is Mr Bateman's nephew and was born one year after the aircraft disappeared. He is now in his 70s.
Mr Morley told Hawke's Bay Today that until this year he could only assume his uncle's plane had been shot down by the Japanese.
"It was the last flight out of Java as the Japanese advanced further south in their conquest of that part of the world, back in the early 1940s.
"There were two planes leaving that day. The first one reached Broome - the second didn't.
"Some search was carried out, but given the tense situation in the area it wasn't as extensive as it might have been, because they were afraid of losing another plane."
However, in February aviation historian Phil Vabre made a post on an internet forum announcing Circe's fate had been uncovered.
The Civil Aviation Historical Society vice-president is writing a book about Qantas Empire flying boats such as Circe.
As part of his research, he collaborated with Japanese researcher Osamu Tagaya, who had access to the Japanese military archives.
"It can now be confirmed for the first time that Circe was shot down by a Japanese Betty bomber based at Denpasar, Bali," the post said.
Records showed the Betty was on a maritime patrol when it spotted and fired on Circe, shooting it down, about 320km south of the Java coast.
Mr Morley's younger brother, Alan Morley, who lives in Sydney, saw the forum post and contacted Mr Vabre for further information.
The brothers decided to hold a presentation of Mr Vabre's findings to Mr Bateman's extended family at Hawke's Bay and East Coast Aero Club last weekend.
"We wanted to tell the story to our family and friends, and thought it would be appropriate to do it where he learned to fly."
More than 50 people attended the "emotional" presentation, including about 20 members of Mr Bateman's extended family, and his only child, Jennifer, who came from Sydney.
Well-known in Hawke's Bay aviation circles, Mr Bateman joined the aero club in the early 1930s.
Club president Bruce Govenlock said he was fascinated by Mr Morley's presentation and the club was still searching its records for information about Mervyn Bateman.
"To think he [Mr Bateman] was a civilian operator right in the thick of an advancing front line like that ... it was a real stroke of bad luck."