Brian just announced the death of his spouse, Melinda Kae Ledbetter Wilson ... and their kids say she died peacefully Monday at home. An official cause of death is unknown... and the exact circumstances surrounding her death haven't been revealed either.

In a heartfelt Instagram post, Brian says ... "Melinda was more than my wife. She was my savior. She gave me the emotional security I needed to have a career."

Brian continues ... "She encouraged me to make the music that was closest to my heart. She was my anchor. She was everything for us."

The couple adopted five children together and Brian says they are all in tears and are lost.

Brian and Melinda first met way back in 1986 when she sold him a Cadillac ... dating on and off for a couple years until rekindling their romance in 1992 and getting hitched in 1995 at Wayfarers Chapel in Rancho Palos Verdes, CA.

Their relationship even inspired a biopic ... 2014's "Love & Mercy" starring John Cusack as Brian and Elizabeth Banks as Melinda.

Briana and Melinda's kids are remembering her as "a force of nature and one of the strongest women you could come by. She was not only a model, our fathers savior, and a mother, she was a woman empowered by her spirit with a mission to better everyone she touched."

They say she taught them lasting lessons, like ... "How to take care of the person next to you with out expecting anything in return, how to find beauty in the darkest of places, and how to live life as your truest self with honesty and pride."

Melinda was 77.