Franklin Delano Roosevelt's father was named James. James had a child with his first wife, and named that child James (nicknamed Rosy Roosevelt). Rosy Roosevelt was the much-older half-brother of FDR. Rosy Roosevelt married Helen Astor and had two children, one named Tadd. Tadd was therefore FDR's nephew, although the two were very close in age.
Tadd, following the pre-set footsteps of the Roosevelt and Astor family lines, went to Harvard for his college studies. He did not graduate, however, instead leaving due to some scandal. He moved to New York, married a Hungarian prostitute, and was completely disowned by his father and his father's family.
Tadd inherited from his mother, from the Astor family, but never touched any of that inheritance. He remained married to the lady from Hungary for 40 years, until his wife's death. When he died, he left his entire estate, including the inheritance from the Astor family, to the Salvation Army.
The basic information is from a footnote in Jonathan Alter's remarkable book The Defining Moment, about FDR.