LFO singer Devin Lima has died after a yearlong battle with stage 4 cancer ... TMZ has learned.

Devin died early Wednesday morning ... according to a family member.

Devin was half of a duo ... the other half being Brad Fischetti. The group originally was a trio, but the third singer, Rich Cronin, died after a long fight with leukemia.

The boy band was popular in the '90s. Their biggest hit was "Summer Girls" in 1999 which peaked at #3 on Billboard Hot 100. Other hits included "Girl on TV" and "Every Other Time." They recorded 2 albums, "LFO" and "Life is Good." The group released the song, "Perfect 10," in the summer of last year.

LFO planned to do a tour in the spring of 2018, but doctors discovered a football-sized tumor sitting on Devin's adrenal gland and pushing against various organs, including his heart. They removed the tumor and discovered it was malignant, and it turned out to be stage 4 cancer.

The band's publicist, Alaina Bendi, told Billboard in 2017 ... "We were really hoping that if this wasn't cancer that we could actually get Devin back in shape so the guys could be on track to get on tour in February. He needs to focus on his health so, LFO's touring will be canceled indefinitely."

Play video content OCTOBER 2017 TMZ.com

Devin was 41.