Monaco's royal family is rocked by mystery death of Prince Albert's cousin, 29, found dead in public gardens - as Ukrainian is arrested

Monaco's royal family has been rocked by the mysterious death of Prince Albert's cousin, who was found dead in a public garden. 

Antoine de Massy's body was discovered on Sunday after he was last seen staggering from a nightclub in the early hours of Sunday morning, according to AFP.  

The 29-year-old was reported missing after he failed to attend a family lunch, local newspaper Monaco Matin reports, and his body was found shortly after. 

Police on Monday arrested a Ukrainian national who was seen with Mr de Massy on CCTV. 

Monaco's Public Prosecutor's office said that the man's role remained unclear and that all possibilities, including an accident, were being considered as police investigate to determine the cause of his death.

He was the grandson of Prince Albert's aunt, Princess Antoinette, making Mr de Massy Albert's first cousin once removed.

The Prince's Palace announced Mr de Massy's death in a statement on Monday: 'Their Serene Highnesses Prince Albert II and Princess Charlène were saddened to learn of the death of Antoine de Massy, aged 29, the grandson of Princess Antoinette, the elder sister of Prince Rainier III,' it read.

'A keen tennis player, he was part of a family history closely linked to the sport in the Principality. Their Highnesses share in the grief of his family and loved ones and offer them their sincere condolences at this painful time.'

Mr de Massy played tennis professionally, and even moved to Florida with his family when he was younger to train at the prestigious Nick Bollettieri Tennis Academy.

He had recently co-founded a tech company called Instant Tech, which connects local businesses, merchants, and clients for instant reservations and payments. 

Despite his royal connections, he preferred to stay out of the spotlight in Monte Carlo's social scene, according to the newspaper Bild.