They are both examples of the 'double possessive' or 'post-genitive' construction, which is used when the noun following the genitive is a person or other animate object. If the noun is inanimate then the double possessive is not used. For example: "I really like the look of the picture."
Double possessives are useful for distinguishing between a genitive of possession and a genitive of description:
1) "The song of Nelly Furtado's" is "Nelly Furtado's song" - the 'of' signifies a genitive of possession.
2) "The song of Nelly Furtado" is "the song about Nelly Furtado" - the 'of' signifies a genitive of description.