Suffering from epilepsy throughout his short life, his illness killed him at the age of 30. He died following an epileptic seizure at the Palace Hotel in Edinburgh. He never married and did not have any children. By his will, the 15th Earl bequeathed the Castle of Mey and its lands and estates out of the hands of the Sinclairs leaving the future Earls of Caithness without a family seat. He left it all to his friend, Mr F. G. Heathcote on the condition that he legally took the name of Sinclair (which he did) and that he lived in the Castle for at least 3 months of each year (which he also did).
References
^"Sudden death of the Earl of Caithness". St James's Gazette. 27 May 1889. p. 8.