Rihanna says her accountant made so many boneheaded decisions that he blew her fortune and she was “effectively bankrupt” by the end of 2009.

The singer claims in new legal docs she had $11 MILLION in cash at the beginning of 2009.  Rihanna says the accountant was not on the ball and she was horrified to learn at the end of the year she had $2 million left. To make matters worse, her expenses doubled, which left her on a financial cliff.

As for how Rihanna blew through $9 million in one year … she says her accountant gave her the green light to buy a house priced between $7 and 7 1/2 million. So she took his advice. She ultimately sold the house for a $2 million LOSS.

She also claims her 2009 tour — Last Girl on Earth Tour — was losing money but the accountant never gave her the heads up.

The legal docs were filed in connection with a lawsuit Rihanna filed against her accountant, claiming gross mismanagement.

BTW … Rihanna has rebounded nicely.  Her net worth is now estimated at $43 mil.