Lisa Marie just filed docs in her divorce from Michael Lockwood, and they contain the bombshell news ... the King's daughter is more than $16 million in the red. In the docs she says most of her debt is unpaid taxes from 2012 to 2015, totaling more than $10 million.

She also says she has a house in the U.K. she's desperately trying to unload because she's defaulted on the mortgage. According to the docs, obtained by TMZ ... that's another $6 mil she owes.

LMP says the rest of her debt is mostly credit cards and unpaid attorneys' bills.

She's revealing all of this because Lockwood is demanding she pay more than $450k for his attorney fees, and she's clearly saying ... I ain't got it, dude.

Fun facts:
- Lisa Marie sold off 85% of Elvis Enterprises in 2004 for $100 million
- The Elvis estate still hauls in revenue north of $20 million annually