Sounds like a discarded Beverly Hills, 90210 plot.

Brian Austin Green is suing Vanessa Marcil-Giovinazzi -- his ex-girlfriend, former costar and mother to his son Kassius, 9 -- for borrowing but never repaying over $200,0000.

TMZ reports that Green (now married to Megan Fox) filed papers in an L.A. Court alleging that he lent General Hospital star Marcil-Giovinazzi money while they were dating -- often $50,000 at a time -- which she promised to pay back.

Green's papers claim that he lent Marcil-Giovinazzi (they both starred in the original Beverly Hills, 90210 together) the bulk of the loans back in 2000. He finally asked his former love for repayment of the loans in November 2011, but to no avail.

The Wedding Band actor, 38, seeks repayment of all the money plus unspecified damages.

Green wed longtime love Fox, 25, in Hawaii in June 2010; the next month his son Kassius then watched his mom Marcil-Giovinazzi, 43, walk down the aisle to wed CSI: NY actor Carmine Giovinazzi.