LAS VEGAS — Mary Wilson, the longest-reigning original Supreme, has died at 76 years old.

Publicist Jay Schwartz says Wilson died Monday night at her home in Las Vegas and that the cause was not immediately clear.

Wilson, Diana Ross and Florence Ballard made up the first successful configuration of The Supremes. She stayed with the group until it was officially disbanded by Motown in 1977.

The group's first No. 1, million-selling song, “Where Did Our Love Go,” was released June 17, 1964.

Motown founder Barry Gordon says he's extremely shocked and saddened to hear of her death. He said the Supremes were “always known as the sweethearts of Motown.”