Khalid Al Qasimi, 39, was found dead at his luxury apartment in upmarket Knightsbridge, west London, after taking high levels of GHB.
He had also consumed “recreational” amounts of cocaine with a man called Yohan Escobar, the hearing was told.
Mr Escobar’s connection with the designer was not confirmed during the 90 minute hearing at Westminster Coroner’s Court today.
The United Arab Emirates Prince, owner of British-based fashion label Qasimi, was found dead on the morning of Monday July 1st by his cleaner Maria Kisaohanyan, the inquest heard.
His family, including his twin sister, were said to be heartbroken by the death of the fashion designer who was described as “on top of his career and on top of the world”.
A family representative said: “Khalid’s passing is still a shock to us all. We mourn the loss of a son, nephew and brother.
“Khalid had a unique vision, a commitment to causes, incredible taste and a beautiful soul. We take comfort that through his flourishing Qasimi label, Khalid’s brilliant, creative, compassionate spirit lives on.”
Mr Al Qasimi, referred to throughout the inquest as Khalid, was last seen on CCTV at his home the day before his death, according to security staff.
Cleaner Ms Kisaohanyan had let herself into the apartment with her key and found Mr Al Qasimi sitting upright on the floor by the corner of the sofa.
Ms Kisaohanyan initially thought he was sleeping, but when she touched his neck she realised something was wrong, the inquest heard.
She told the building manager: “Dial 999! He is dead. He is dead,” the hearing was told.
The inquest heard she was employed by Mr Al Qasimi for several years at his apartment where she worked five hours per day from Monday to Friday.
Summarising her statement to the court, Coroner Bernard Richmond QC said: “She thought originally he seemed to be asleep.
“His mouth was open; his eyes were half open, but he was not snoring which she regarded as unusual because he usually snored.
“She thought he was going to wake up and she decided to check on him. She touched his neck because she was becoming worried and it was cold.
“It was clear to her that something was wrong and she phoned the manager of the building to say ‘Dial 999! He is dead. He is dead.'”
A security man was called to the apartment to help and paramedics also arrived, but “it was plain it was too late,” the court heard.
In her statement read to the court, Ms Kisaohanyan said: “He was full of life, on top of his career and on top of the world, very open-minded and very clever.”
Relatives of the Prince were not present at today’s hearing where the cause of his death was determined as “drug-related”.
He was found with more than 300mg of GHB in his bloodstream, according to a toxicology report by Dr Susan Patterson.
Det Sgt Adrian De Villiers, who investiged the death, said the last person to see Mr Al Qasimi alive was most likely a man named as Yohan Escobar.
Giving evidence, DS De Villiers told the inquest: “We were able to identify the person who had probably last seen him alive. That person was called Yohan Escobar.”
Mr Escobar, who the inquest heard was never a suspect in Mr Al Qasimi’s death, told police he had seen him taking both GHB and cocaine and that he himself had done so as well, the inquest heard.
He said he thought Mr Al Qasimi was asleep when he left the flat on June 30 because he was snoring, and he was found dead in the same spot the following morning.