answer:It’s correct to express the possessive, which this is. It’s also redundant, but idiomatic (meaning that’s just the way we say it): we’d say “I’m a big fan of yours” and not “I’m a big fan of you.” With a person’s name, the double possessive can safely be omitted, but we do hear it all the time, as in your example. Curiously, we don’t use it with inanimate things: “She’s a big fan of baseball,” “I’m a big fan of ambiguity.” Yet it would still be there to stand in for the “of” if you reworded it: “He’s baseball’s biggest fan.”