12/22 12:50 PM PT -- Trina released a statement on her ex-husband's passing, saying ... "a chapter permanently closed for my sons and I. For over 16 years, Gabe Solis was an essential part of our lives."

She also apologized to friends and family who weren't aware of Gabe's situation and found out through the media ... specifically the Solis Family. Trina added ... "He was a father to my boys, a son, brother, and friend to many and I would appreciate privacy and respect as we grieve his unexpected departure."

Trina Braxton's ex-husband, Gabe Solis, has died after a battle with cancer ... TMZ has learned.

Sources tell us Solis died Thursday in Texas, where he hails from, and we're told he was surrounded by friends and family.

Trina and Gabe wed in 2003 but divorced in 2015, and their on-again, off-again relationship was a frequent topic on the family's reality show -- "Braxton Family Values" -- even after they divorced.

The former couple also appeared on an episode of "Iyanla: Fix My Life" earlier this year -- more than 2 years after their split -- to hash out their issues and work on a plan to finally move on.

In the episode, Gabe confronted Trina about her verbal abuse and bullying and let her know how it affected him during their marriage. Despite their rocky road ... the 2 remained close friends.

We're told Gabe's health issues were kept under wraps and his passing comes as a surprise to many close to the family.

He was 43.

RIP