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 behind the New National Museum along the Boulevard du Larvotto on Sunday.
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 reported, and his body was found shortly after.
Police on Monday arrested a Ukrainian national who was seen near where Mr de Massy's body was found 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, the grandson of Princess Antoinette, the elder sister of Prince Rainier III.
'A keen tennis player, he was part of a family history closely linked to the sport in the Principality.
Antoine de Massy's body was discovered on Sunday in a public garden in Monaco
He was the first cousin once removed of Monaco's Prince Albert II
'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 moved to Florida with his family when he was younger to train at the prestigious Nick Bollettieri Tennis Academy, with hopes of making it to the Olympics.
In a 2012 interview with Vogue Italia, he said his dream was to 'become number one in the world,' adding, 'even in the top 20 wouldn't be bad!'
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.
One of his last public appearances was at the traditional Te Deum Mass for Monaco's National Day in November 2025.
His father, Baron Christian de Massy, is often referred to as the black sheep of the family, having been kicked out of school and banished to Argentina for causing too much trouble in his youth. Dubbed a playboy by local media, all four of his marriages ended in divorce. He is rarely ever seen at social events with the Monaco royal family.
It comes after a bombing attack rocked Monaco this summer, injuring Ukrainian business tycoon Vadym Yermolaiev, who has ties to Russia.
His body was found in a park along the Boulevard du Larvott in Monaco (street view)
Antoine de Massy (top right) with members of Monaco's royal family
A woman and a child who were with him were also injured.
Days after the attack, a woman suspected of trying to kill the businessman was found dead in Ukraine with gunshot wounds to her head, according to Ukraine's Security Service.
A Ukrainian military intelligence officer confessed to killing the bombing suspect, Anastasiia Berezovska, with the help of a former law enforcement officer, the security service, known as the SBU.
Both men were detained on suspicion of murdering Berezovska, a Ukrainian national whose last known residence was in Germany, according to authorities.
They also 'may have been involved in planning' last week's bombing, Monaco prosecutor Stéphane Thibault said at the time.
The attack shocked Monaco, a coastal playground for the rich and famous known for its tax-friendly incentives, royal family and Formula 1 Grand Prix.
Ukraine is believed to have carried out attacks and targeted killings of Russian figures in the course of the war; however, those attacks have largely been confined to Ukrainian or Russian territory.
It comes after a bombing attack rocked Monaco this summer, injuring Ukrainian business tycoon Vadym Yermolaiev
Fesenko noted that at the end of April, Yermolaiev’s son, Artur, settled charges brought against him in Estonia related to an alleged phone scam that took in more than 100 million euros from citizens in multiple European countries between 2019 and 2022, according to local media reports.
As part of the deal, the younger Yermolaiev paid an 8.5 million euro fine.
Monaco's head of state, Prince Albert II, described the bombing as 'an odious act.'
Yermolaiev built his fortune through the Alef Group, a diversified business that includes commercial real estate, manufacturing and agriculture.
Sanctioned by Ukraine in 2023 for his ties to Russia, Yermolaiev has said he renounced his Ukrainian citizenship nearly a decade ago.