Australian Royalty: Genealogy of the colony of NSW

It is not true that Prosper, or his younger sister Melanie, are the children of Julie de St Laurent. It is therefore also not true that Prosper is the son of a liaison between Julie de St Laurent and Edward Duke of Kent, the father of Queen Victoria. This mistaken belief has become legend due to the incorrect assertion that Julie de St Laurent was the wife of Prosper's father André Charles de Mestre. It is true that André Charles lost his head and his life on the battle field at Martinique, and that Prince Edward was at Martinique at the time, but this death was of no significance to either Prince Edward or Julie de St Laurent.

The other incorrect assertion about Prosper's birth was made by Prosper himself in a letter dated 25 March 1830 and written to both the Collector and the Comptroller of Customs of the Colonial Government of New South Wales stating his claim to be a British subject. In this letter he made a statement that claimed he had been born in 1793 while his parents had been fleeing the French Revolution on a British ship bound for Martinique.[8] This statement was made to protect Prosper's commercial interests when he had applied to register a British ship, and the legality of his claim to hold a British-flagged ship was questioned. Chief Justice (Sir) Francis Forbes of the Supreme Court of New South Wales, after various letters and evidence (including Prosper's letter to the Collector and Comptroller of Customs), ruled that because Prosper had been born on the high seas in a British ship he was a British subject, and therefore his application must succeed. However Prosper was not born on the high seas in a British ship, but was born on dry land in France. Prosper's lie was not exposed in his life-time. Neither was it exposed by his many children & descendants in the intervening years, who had always believed that he had told the truth. It was exposed in 2008, nearly 180 years after the statement was made, by his great, great, great granddaughter Maree Amor (née Wade) when she was finally able to track down the record of his baptism.

Prosper arrived in the colony free as supercargo aboard the ship 'Magnet' on 16 apr 1818.

On 1 March 1821 31-year-old Prosper married 19-year-old Mary Ann Black (1801–1861) at St Philip's Church, Sydney. Mary Ann, not yet "of full age" and 12 years his junior, was the daughter of the privateer (state-sanctioned pirate) and ship's captain John Black, and the former convict Mary Hyde who in 1855 took the Commissioners of City of Sydney to the House of Lords and won. Mary was also the stepdaughter of Simeon Lord, an emancipist, and a pioneer merchant and magistrate in early Sydney. Mary Ann was a good catch for de Mestre, with her stepfather Simeon Lord's connections being invaluable to Prosper's business dealings.

Mary Ann Black of Sydney was married to Prosper de Mestre a merchant of Sydney by Rev. W. Cowper at Sydney on 26 Feb 1821, the licence having been obtained 26 Feb 1821

"MARRIED. - By Special License, at the Church of St. Philip, Sydney, by the Rev. Mr. COWPER, on Thursday morning last, P. DE MESTRE, Esq. to Miss BLACK, of Macquarie-place."

Prosper's commercial interests in the Colony of New South Wales were mainly in shipping and whaling, but he also became active in wider commerce. In June 1823 he was elected a director of Sydney and Van Diemens Land Packet Company. In June 1825 he was elected to the committee of the Agricultural Society of New South Wales. Prosper was a director of the Bank of New South Wales (1822–23, 1826–28, 1829–42), and in the 1830s he was a director of the Australian Marine Assurance Company. In 1840 he was a founder of the Mutual Fire Insurance Company of Sydney.

Prosper de Mestre was a benevolent man, who regularly donated to charities. These included the Benevolent Fund, and the Catholic Chapel Fund, which financed the building of St. Mary's Cathedral, the first Catholic Church in the community. He had been born a Roman Catholic, but he also became active in church affairs of the Church of England, the religion of his wife and children, and the official religion of the Colony. In 1836 as a supporter of the Church of England he joined the committee in opposition to the proposed National School System and in 1841 he became a trustee of Christ Church St. Laurence.

Prosper was also involved in many real estate dealings. His first property purchase was in 1821 in George Street, Sydney, an allotment that had been received by his brother-in-law John Henry Black as his dower, and that was next door to a portion of land that his wife Mary Ann had also received as her dower on her marriage, and had been held trust by her stepfather Simeon Lord from an original land lease given to her father Captain John Black. It was on the George Street properties that his wife had been born, and on the George Street properties that Prosper resided with his family, and also had his counting house. The site is found today at a small lane named De Mestre Place. In addition to the George Street properties, Prosper applied for his first land grant, and on 7 September 1821 was granted 700 acres at West Bargo, near Camden. The grant was on condition that he maintain and employed 7 convicts on the property. In 1831-32 he bought a section of land (the Helsarmel Estate) at Leichhardt from a Captain Piper. In 1824 (prior to his 1825 naturalisation) Prosper De Mestre was first promised a land grant by Governor Thomas Brisbane. 1300 acres were authorised on the southern shore of the Shoalhaven River near present day Nowra in 1829. However he did not receive the grant until 1836 from Governor Sir Richard Bourke, and he named the property "Terara". The homestead Mill Bank House which still stands in Millbank Road, was probably erected at this time, and a village named Terara soon began to develop. He eventually owned several houses in Sydney, including his main house, 32 acres at Petersham, and many farm allotments. To consolidate some of his business investments, on 31 May 1837, at "the Premises lately occupied by Prosper De Mestre" at George Street he sold at auction a number of properties, being: 3160 acres at Brisbane Water; 700 acres in the parish of Holdsworth; building allotments in Kent St, Sydney; four 25 acre farms at Lane Cove; 640 acres at Camden; and 3200 acres at Ellulang. He no longer needed to live in the George Street property as he had moved his residence to the corner of Liverpool and Elizabeth Streets, Sydney as he had purchased an "excellent mansion" overlooking and situated at the south end of Hyde Park. Finally he also received another land grant of 1280 acres called Yerrigong on the Calymea Creek about six miles west of Terara granted by Governor George Gipps on 17 February 1841.

On 31 May 1837 he also sold 50 shares in the Australian Marine Assurance Company, the Hoffan's Cordials business, and a lithographic press. Then, due to the depression of the early 1840s, and failing health, Prosper become insolvent in 1844. Most of his land and property needed to be auctioned to pay his debts. As the George Street property had been her dower, his wife Mary Ann questioned whether it should be included in the sale. Her solution was that the more valuable George Street property could be included in the sale, if the Shoalhaven properties were not. In exchange she also asked for "the whole of the plate, horses etc., etc., on the establishment in Liverpool Street, the six cows, horse and cart at Helsarmel", and to be"permitted to occupy the thirty-two acres at Petersham until the house at Shoal Haven can be rendered fit for the residence of my family." His house in Liverpool St, and its "elegant Household Furniture", was sold by auction on 16 May 1844, and the family was moved to briefly to Petersham and then onto Terara, which Prosper had initially developed as a hobby farm.