I suggest that the new councillor has a private conversation with the Chair to explain the situation. It's also worth checking to see whether the job description is lurking somewhere on the Council's website from the last time it was advertised as a vacancy.
As a last resort, the Council would be obliged to provide it in response to a Freedom of Information request, so perhaps the Chair and Clerk could be made aware of this in a calm and sensible way, to help them to understand the situation. I'm rarely in favour of the use of FoI within a Council, as I see it as the start of a slippery slope, so hopefully that would not be necessary.