The longtime broadcaster's wife, Nora, announced his passing on social media Friday ... thanking fans for their love and support in a poignant Facebook post. She didn't get into the exact circumstances of his death, but did speak on his legacy.

Nora wrote ... "He was more than just a beloved husband, father, TV host, musician, and entertainer; he was a beacon of hope and joy for countless people. His infectious charisma and dedication to promoting Latino music and culture left a large mark on the world."

She added, "Johnny's spirit will continue to live on through the countless lives he touched and the legacy he built" -- while going on to ask fans to remember the joy he brought about.

In addition to being a TV host ... Johnny was also a singer, but was best known for hosting the show, "The Johnny Canales Show," where a 13-year-old Selena made one of her first live TV performances in '85.

His show became known for highlighting emerging talent from Mexico and the U.S., including La Sombra de Chicago, La Mafia, Mazz, Intocable, Grupo Pegasso De Emilio Reyna, Fama, Jaime y Los Chamacos, Jennifer Peña, among countless others.

A number of fans have flooded Nora's announcement with condolence messages, thanking Johnny for his contribution to the Tejano music scene. One fan added ... "He was our childhood and a staple in the industry and his legacy is unprecedented." He was 77.