Leighton Meester is suing her mother and now RadarOnline.com has exclusively learned she wants her younger brother to live with her instead of with their mom.

Leighton, 25, regularly sent money to her mother, Constance Meester, to help pay for her brother's health needs, but the in the lawsuit filed on July 22, 2011, Leighton claims her mother used the money to get cosmetic surgeries for herself instead.

"Leighton is disgusted by her mother and is determined to get her brother Lex out of that situation," an insider told RadarOnline.com.