Weston Cage & Nikki Williams -- DIVORCE FINAL ... She Keeps Her Wedding Ring

Nicolas Cage's son Weston and his wife Nikki Williams are officially divorced, TMZ has learned -- but the crazy part ... she gets to keep her wedding ring, despite promising to PAWN IT OFF.

As we reported, 22-year-old Weston filed for divorce back in 2011 -- not really shocking, considering they were both arrested for domestic violence against each other after they tied the knot earlier that year ... following a two-week engagement.

The divorce is now final -- but according to the order, obtained by TMZ, 24-year-old Nikki gets to keep her wedding ring ... along with the rights to her entire song catalog, including a track called "Pawn My Wedding Ring."

The song was written last year, after Weston filed for divorce, and it contains the lyrics -- "It started perfect, you were a different person / But you changed on me after the honeymoon was done."

It continues ... "And because it's not worth anything / I'm about to pawn my wedding ring / Get rid of everything that was right or wrong." See? It's right there in black and white.

Meanwhile, Weston gets to keep his musical equipment, bank account, and songs ... including fluffy uplifting hits like "Souless Eyes," "Vampire Sentiment," and "Heathen Sanctuary."