It wasn't until builder Ray Hollingsworth, who has been renovating the building for the Presbyterian church, unscrewed the door plate while restoring an old door that the hidden message was revealed for the first time.

The note had been written by historian Les O'Callaghan probably in 1942 while he was a boarder at the Spence Street property, a message his widow Elizabeth O'Callaghan says he had probably forgotten about.

Mr O'Callaghan, who passed away in 2014 aged 96, was known to his friends as Mr History and he spent more than three decades as the president of the Warrnambool and District Historical Society.

Written on the back of the door plate in pencil, Mr O'Callaghan scribbled his name, birth place, occupation and how long he'd lived at the address.

Mr Hollingsworth said that when he showed the door plate to Mrs O'Callaghan she said: "fancy that, he's been gone four-and-a-half years and he's still speaking to me from the grave".

"I still am amazed that he took a door plate off and wrote on the back and put it back again," she said.

"That's what you call leaving your mark".

Mrs O'Callaghan said her husband was always very conscious of making history as an individual.

"I find it quite an emotional thing for someone to suddenly produce something with your husband's writing on it," she said.

"It certainly brings back memories."

Mrs O'Callaghan said she wasn't surprised by her husband's hidden note because he always used to tell stories from his time living there from 1939 to 1942.

Although she said he never mentioned his hidden message.

"He was an historian before his time wasn't he," Mr Hollingsworth said.

Mrs O'Callaghan said her husband loved the boarding house and devoted four pages of his autobiography to his time there.

She said he'd lived there until around the time he married his first wife during World War II, and at the time worked at Kraft Walker Cheese factory at Allansford where he became known for his pioneering work as a microbiologist.

"Les didn't have any transport. He used to ride a motorbike and it was confiscated during the war for the war effort. They just took it from him," she said.

Mr O'Callaghan was born in Balmoral in 1918 and moved to Warrnambool at the age of 13 when he won a scholarship to study at the technical school. He'd boarded at a number of houses in the city before moving to the one in Spence Street.

She said the boarding house was probably built in the 1880s as a shop. Records show the property was first purchased in 1871.

The boarding house was run by May and Sam Taggart - a well-known tailor - and out the back they kept a cow.

"In those days when you had a cow in town you took it to Albert Park during the day for the pasture and just brought it back at night and milked it, kept it over night and milked it the next morning and then you took it back to what was called the common pasture land," Mrs O'Callaghan said.

The door plate reads: "Leslie Alexander O'Callaghan lived here for some years 1939-1942AD. His occupation was as assistant bacteriologist for Kraft Walker Cheese Coy at Allansford. Born at Balmoral, 40 miles north of Hamilton, Victoria."

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