Princess Elena accused her son, Nicholas Medforth-Mills, of disregarding "the privacy, suffering and dignity" of her 96-year-old father, former King Michael, in a statement issued by the royal house.
Her comments came after the royal house filed a complaint to Swiss police Tuesday alleging Medforth-Mills had tried to force his way in to his grandfather's home in Aubonne, Switzerland, and had "physically and verbally aggressed" three staff members.
"My son has shown contempt for Romania, her people and the principles of the Royal House. For me, his mother, this behavior is devastating," she added.
Medforth-Mills accused his relatives of trying to discredit him and playing "a dirty game."
"These statements gravely harm the image of what the Royal House should be, its history, its values and its dignified stance which my grandfather and his forebears tried to live by and keep," Medforth-Mills said in a statement on Facebook.
"I, Nicholas, just wanted to see my grandfather and say goodbye to him in a peaceful, respectful and Christian way."
Michael is suffering from leukemia and skin cancer, and the royal house recently announced that his condition had deteriorated. Romania is a republic and the monarch no longer has any constitutional powers, but Romanians associate their royal family with an elegance and dignity that they say their politicians lack. The head of the royal house looks after the family's properties and bestows honors.
Medforth-Mills, 32, Michael's only grandson, was one of the most popular members of the Romanian royal family. His good looks, down-to-earth manner and love of cycling and ecology endeared him to Romanians.
But in August 2015 his grandfather suddenly stripped Nicholas of his title and his position as third in line to the throne behind his aunt and his mother. Shocked Romanians speculated that a jealous relative had sought to edge him out of the succession.
It later emerged that Nicholas may have fathered a child with a Romanian woman, a situation that was said to have affected Michael badly as an echo of his own unhappy childhood. His father, Carol II, married three times and was forced to give up the succession to the throne over an affair while he was still married to Michael's mother, leaving Michael to be king when he was only 5. Carol later did become king.
Princess Elena said Thursday that Michael was refusing to see his grandson over his failure to clarify the paternity of the child, now 2.
Many Romanians took to social media to defend him, saying as the ex-king's only grandson he should have been permitted to see his dying grandfather and have the opportunity to reconcile.
"When successions are involved, it's normal to have a drama, it's something Shakespearean" Stelian Tanase, a commentator told The Associated Press, adding: "However, I would have expected a level of decency in Romania, which is not a monarchy."
"The Royal House lives from prestige. The king has enormous prestige, but others have to earn it."
Michael is one of the few leaders from the years of World War II still living. He occupied the throne during 1927-1930 and again from 1940 until 1947, when communists forced him to abdicate.
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