As the prime minister noted in a speech in Perth on Wednesday: "It's a long time since one of my family was in Cornwall".

Mr Morrison's ancestor William Roberts - who the prime minister described as his "fifth great-grandfather" - was born in the English county in 1755.

Roberts was tried at the Bodmin assizes in Cornwall for stealing "five pound and a half-weight of yarn" belonging to William Moffatt, from the nearby market town of Launceston.

The theft made the local newspaper in August 1786.

He was initially placed on the hulk Dunkirk a month later, moored at Plymouth, before being transferred to the convict transport Charlotte and later put on board the Scarborough - one of the 11 ships in the First Fleet.

Roberts arrived at Sydney Cove in January 1788 and soon gained respect and attention for his carpentry skills.

He had two children with another convict Kezia Brown, who arrived on the Neptune, before they were married in August 1793 at St Philip's church in Sydney, by the colony's first minister, Richard Johnson.

The family settled in the Windsor area, northwest of Sydney, becoming stalwarts of the community with family members holding rural property there until the 1950s.

The prime minister is related to Edward Roberts, the last of William and Kezia's children, born at the family property Hobby Farm in April 1813.

Edward inherited the farm, which official records show in 1822 was planted to wheat, maize, barley, potatoes, an orchard, and ran cattle and pigs.

William Roberts died aged 65 in February 1820, with wife Kezia spending 34 years as a widow.

William and Kezia are buried at St Matthew's Anglican church in Windsor.

(Ed. note: Information sourced from the Fellowship of First Fleeters and the family history book, A Rich Inheritance. The author of this story is also a descendant of William and Kezia Roberts.)

Australian Associated Press