A 42-year-old man has been charged with involuntary manslaughter in connection with the death of Monaco royal Prince Albert's first cousin once removed, Antoine de Massy.

The suspect -- who is a Ukrainian national living in Monaco for 3 decades -- was brought before a judge on Wednesday and denied the charges against him, which included failure to assist a person in danger ... Monaco Life reported.

With an investigation now open into "the precise sequence of events that led to Antoine de Massy's fall" ... Monaco's Prosecutor General Stéphane Thibault said that the alleged crimes "may have been committed at different times."

De Massy was found dead in a park on Oct. 25 ... he was only 29 years old.

Since his death ... Prince Albert and his wife, Princess Charlène, have spoken out about his shocking passing.

They wrote 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."

They added ... "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."