no one (else)

Not necessarily, Ms Tan.

No one besides me knows the answer to the question.

No one else besides me knows the answer to the question.

Perhaps it's used to add some emphasis.

Hi JTT
Can I infer that my sentence is wrong?

No, not at all. In that collocation, I'd say that it's probably the more natural/common way of saying it.

Thanks, JTT, for confirming that my sentence is fine.