A famous New York City art dealer with ties to Michelle Obama has been found dead in an apparent homicide.

Police in Rio de Janeiro, Brazil, have opened a probe into the deadly stabbing of Brent Sikkema, 75.

The police believe Sikkema was murdered during a robbery, and that he was stabbed to death with either a box cutter, a screwdriver, or a pair of scissors. No arrests have been made.

"Agents will listen to witnesses, are looking for more information and will carry out other measures to clarify the case," police said.

"Great sadness"

The sad news of the death was confirmed by Sikkema's gallery, Sikkema Jenkins & Co.

The gallery was opened as Wooster Gardens in SoHo in 1991, before being renamed and moved to its current location in the artsy Chelsea neighborhood.

"It is with great sadness that the gallery announces the passing of our beloved founder,” the gallery said, adding: “The gallery grieves this tremendous loss and will continue on in his spirit.”

Sikkema, who was gay, was known for celebrating progressive artists like Kara Walker and Jeffrey Gibson.

The Brazilian photographer Vik Muniz, who was friends with Sikkema for decades, applauded his gallery as "one of the first....to have a contingent of artists who were half white, half black, half woman, half man."

His body was found by his lawyer, Simone Nunes, who called him "a wonderful person, very kind, generous, defender of social issues."

Nunes was entrusted with watching Sikkema's home in Rio's exclusive Botanical Gardens neighborhood when he was away.

She went to check on him Monday night after he stopped answering her calls - and found him dead in his bed.

Ties to Obama

The Morrison, Illinois, native was educated at the San Francisco Art Institute and began his career at the Visual Studies Workshop in Rochester, New York.

He owned Vision Gallery in Boston before founding the Manhattan gallery that bears his name.

His circle of acquaintances included former First Lady Michelle Obama, who was photographed with him in a picture shared on Instagram.

Sikkema is survived by his husband and their 12-year-old son.

“We can confirm the death of a U.S. citizen in Rio de Janeiro,” a State Department spokesman said. “We offer our sincerest condolences to the family. We are providing all appropriate assistance to the family. Due to privacy considerations, we have no further comment.”