Authorities were awaiting autopsy results Tuesday in the death of a charismatic hotel heir found in his Union Square apartment from an apparent drug overdose.

Police responded to a 911 call around 8 p.m. Sunday and found Charles Denihan, 28, unresponsive and with no signs of trauma. Drugs, including narcotics, were recovered at the scene, police said.

He was pronounced dead at the scene.

Denihan was the son of Benjamin "Patrick" Denihan and co-CEO with his sister, Patricia Barrett, of The Denihan Hospitality Group, a family business founded in 1963 that operates numerous hotels and restaurants, including The Surrey, The Affinia Shelburne, The Affinia Mahattan and The James in NYC.

Denihan "was an active member of the family business, and was heavily involved in key technology and music ventures," said a family spokeswoman.

The Denihan family's first venture in New York City was a luxury laundry and dry cleaners founded in 1927 by the deceased's great-grandfather, an Irish immigrant. Known as "cleaners to the stars," the firm catered to Marilyn Monroe, Hattie Carnegie and the Vanderbilt family.

"We are devastated at the tragic and sudden loss of Charlie," said a statement issued by the family. "He was a loving and remarkable son, brother, nephew, cousin, godfather and friend. In this tragic time, we ask that you remember him in your prayers and respect our privacy as we mourn his passing."

Charlie Denihan is listed as being a 2004 graduate of The Deerfield Academy and attended Cornell. His Instagram handle described him as being interested in hotels, travel, NYC, sports, music, web development "and Fun. . . . best not be allergic to fun."