Thanks for the welcome.
As several posters have pointed out, the sentence is correct, as punctuated. The example used in the article I read illustrated the correctness of the "double possessive" as follows: If one were describing, for example, a portrait of Frank versus a portrait owned by Frank, the only acceptable distinction would be the possessive apostrophe in the latter case.
As pointed out by some, the test in such cases is the substitution of a pronoun.