The inquest into the death of Thomas Kingston, the late husband of Lady Gabriella, will examine whether his death was linked to new medication he was taking.
The financier, who was found dead at his parents' home in the Cotswolds on 25 February, died aged 45 from a "traumatic head wound" and a gun was found near his body.
During a pre-inquest review hearing at Gloucestershire Coroner's Court on Tuesday 8 October, Martin Porter KC said the Kingston family had been "advised that there could be a connection" between medication he had taken and his state of mind before his death.
Mr Porter told the court: "The inquiry shouldn't be limited to the very final cause of death, which is clear and obvious."
He said the inquest should include "Mr Kingston's state of mind and whether that state of mind was affected by medication he had taken".
Mr Porter added: "In support of my submissions, the family have been advised that there could be a connection… for your court to investigate."
Katy Skerrett, senior coroner for Gloucestershire, said the "recent prescription… should be part of the scope", adding: "I agree with Mr Porter, however I do caveat strongly that whether a causative link will be established is a very different matter."
Thomas's parents attended the hearing and the court heard his father Martin Kingston will give evidence to the inquest on behalf of the family. Lady Gabriella was not present at the hearing.
At the first inquest in March, Ms Skerrett outlined the circumstances of the financier's death in a short hearing at court, saying: "Mr Kingston was visiting his parents' home in the Cotswolds. On February 25 2024, he ate lunch with his parents. His father went out to walk the dogs.
"On his return Mr Kingston was not in the house and after approximately 30 minutes his mother went to look for him. His father forced entry on a locked-out building when no reply could be gained.
"He found Mr Kingston deceased with a catastrophic head injury. A gun was present at the scene. Emergency services were called. Police are satisfied the death is not suspicious.
Thomas was the son-in-law of Prince and Princess Michael of Kent. He proposed to Lady Gabriella in August 2018, with the pair walking down the aisle in May 2019.
Shortly after his death, Gabriella, 43, issued a joint statement alongside Thomas' parents, Martin and Jill, as well as Thomas' sisters Joanna Connolly and Emma Murray.
It read: "It is with the deepest sorrow that we announce the death of Thomas Kingston, our beloved husband, son and brother. Tom was an exceptional man who lit up the lives of all who knew him. His death has come as a great shock to the whole family and we ask you to respect our privacy as we mourn his passing."
Thomas's funeral took place earlier this year at the Chapel Royal at St James's in London, followed by a reception in St James's Palace. There were 140 people in attendance, including Thomas's widow, Thomas's family, the Duke of Kent and Princess Alexandra and the Prince of Wales.
HELLO! understands the one-hour service was led by the Sub-Dean of the Chapels Royal, the Revd Canon Paul Wright, with a sermon from the former Bishop of London, the Rt Revd Richard Chartres.
In June, meanwhile, an intimate celebration of service was held at St Mary Abbots Church in Kensington. The service was attended by close friends and family in addition to several members of the royal family.
A spokesperson for the Kingston family said: "Lady Gabriella and the Kingston family have been deeply touched by the outpouring of love, kindness and support they have received over the past difficult months.
"They were grateful today for the chance to celebrate – and give thanks for – the life of a wonderful man, among so many of those who knew and loved him too."