[6] His military career included cornet 2nd Dragoon Guards and reaching the rank of lieutenant colonel in the Reserve Cornwall militia.

[7] His second son Henry Trevanion Bettesworth (1804–1855) married 4 February 1826[8] his distant cousin[9] Georgiana Augusta Leigh (1808–1866), a daughter of Augusta Leigh (elder half-sister of Lord Byron) but in 1829 ran off with his sister-in-law Medora)[10] to the Continent, where he eventually separated from her and died in 1855.

[5] Bettesworth-Trevanion rebuilt Caerhays as a Gothic-style castle using the design of the Anglo-Welsh architect John Nash.

As a consequence of his extravagance, Bettesworth-Trevanion fell heavily into debt, fleeing to Paris,[11] forced to live abroad.

The books stress both the magnificence of Caerhays and the ruinous cost to Trevanion of the rebuilding: a well-informed neighbour remarks that "the madman's nigh on bankrupt".