On 12 August 1822, his half-brother committed suicide He succeeded his half-brother as 3rd Marquess of Londonderry in 1822.
The following year Lord Londonderry was also created Earl Vane and Viscount Seaham, of Seaham in the County Palatine of Durham, with remainder to the heirs male of the body of his second wife.

His half-brother's death also meant the end of his diplomatic career.
He quit the diplomatic service in 1823.
Queen Victoria had a low esteem of Londonderry's abilities as a civil servant.
She said that he should, in her opinion, not be given any post of importance.
On 12 August 1822, his half-brother committed suicide He succeeded his half-brother as 3rd Marquess of Londonderry in 1822. The following year Lord Londonderry was also created Earl Vane and Viscount Seaham, of Seaham in the County Palatine of Durham, with remainder to the heirs male of the body of his second wife.
His half-brother's death also meant the end of his diplomatic career. He quit the diplomatic service in 1823. Queen Victoria had a low esteem of Londonderry's abilities as a civil servant. She said that he should, in her opinion, not be given any post of importance.
Charles Vane, 3rd Marquess of Londonderry