Nikki Reed Files for Divorce from Paul McDonald

"Twilight" star Nikki Reed has filed for divorce from former "American Idol" contestant Paul McDonald ... TMZ has learned.

In the divorce docs, obtained by TMZ, Reed cites irreconcilable differences. She's also asking the court to deny McDonald spousal support. It was the first marriage for both. The couple had no kids together.

Reed and McDonald announced they were splitting back in March ... and revealed they'd already been living apart for 6 months.

Interestingly, even though several reports had the couple getting married in October 2011 -- in the docs their marriage date is July 14, 2011.

Despite the split, Nikki and Paul have continued working on an album together. Not weird at all.