Complex sentence: He was known as Lord Hervey from 1723, upon the death of his elder half-brother, Carr, the only son of his father's first wife, Isabella, but Lord Hervey never became Earl of Bristol, as he predeceased his father.
Split into simpler sentences: He was known as Lord Hervey from 1723, upon the death of his elder half-brother, Carr, the only son of his father's first wife, Isabella. But Lord Hervey never became Earl of Bristol, as he predeceased his father.