'Passions' Star Brook Kerr Files For Divorce ... NOT from a Gay Half-Brother

"Passions" star Brook Kerr is pulling the plug on her marriage, TMZ has learned ... but unlike her character on the show, her husband isn't also her secretly gay blood relative.

Brook filed the docs in L.A. County Superior Court this month against husband Christopher Warren, citing irreconcilable differences. The couple married 22 years ago, but separated in 2009.

Fun fact: the couple only has one son ... 22-year-old Chris Warren Jr. ... who starred in all three "High School Musicals."

Fun fact #2: Brook was originally cast as Tara in "True Blood," but was eventually replaced by Rutina Wesley.