Anna Anderson (born Franziska Schanzkowska) claimed for decades to be Grand Duchess Anastasia Nikolaevna, youngest daughter of Tsar Nicholas II. Some supporters believed her; others, including surviving Romanov relatives, rejected her.
Post-Soviet DNA testing (1990s) on Anderson's tissue samples and on remains from the Romanov grave conclusively proved she was not Anastasia. She had no access to genuine Romanov family secrets—her "knowledge" came from public accounts, newspapers, and coaching by supporters.
Anderson was an imposter; there is no credible evidence she possessed any confidential information about the imperial family.