THE son of an earl shot himself in the head with his father's gun after developing severe mental problems, an inquest was told.

Alexander Carnegie, 20, whose formal title was the Lord Rosehill, died at the family's Rogate farmhouse.

He had suffered from depression and drug-induced psychotic symptons, believing parts of his body were being removed, although his condition was said to be improving.

His father, David Carnegie, 47, the Earl of Northesk, was in America with his wife Jacqueline and her family at the time their son died from a single shotgun wound.

The earl is a Tory whip in the House of Lords, where he is spokesman for the cabinet office, works and pensions.

Alexander's body was found at the family home, Haben Farmhouse at Rogate, by his younger sister, Lady Sarah Carnegie, just a few hours after she had picked him up from the hospital where he was being treated.

Just before he died, Alexander had been playing computer games in his father's office.

His body was found in the attic room at the farmhouse next to where his father stored the shotgun in a locked cupboard. He had left no note.

At the time he died, he had taken 20 anti-depressant pills but the amount was not enough to kill him or make him confused, the inquest in Chichester was told.

West Sussex coroner Roger Stone recorded an open verdict, saying there was not enough evidence to prove the young man had intended to commit suicide.

His father told the inquest Alexander had phoned him and his mother in America just half an hour before he died but had seemed well.

The earl said: "He seemed perfectly normal. As far as I was aware it was normal chit chat."

He added: "I knew there were guns in the house, I do my best to store them properly.

"Part of my security regime is that if I have to find the keys then somebody else does.

"I thought Alexander's ambition at the time was to join the rest of the family in America.

"We will never know if his death was an accident."

In a statement, his sister lady Sarah said: "On the day I picked him up he told me someone else in the ward where he was being treated had killed themselves.

"We have had problems in our family and Alexander had blamed himself for them."

Alexander first developed mental problems while he was in America with his family in June, 2000.

His father had to bring him back to the UK where he was sectioned and taken to Graylingwell Hospital in Chichester for treatment.

He was later discharged after staff believed he had been smoking cannabis.

At the time he died on August 31 this year he was being treated at the hospital as a voluntary patient.

Before falling ill Alexander had worked as a chef and for an engineering firm. He had two other younger sisters, Fiona and Sophie.