Can someone help me solve the following question please?

Let v be a vertex of a d-polytope P such that $ 0 \in intP $ . Prove that $ P^* \cap \{ y \in \mathbb{R}^d \mid\left < y, v\right>=1\ \} $ is a facet of $P^{*} $.

The definitions are: $P^*=\{ y\in\mathbb{R}^{d}\mid\left < x, y\right>\leq 1\ \forall x\in P\} $ and a face of P is the empty set, P itself, or an intersection of P with a supporting hyperplane (i.e.- a hyperplane, such that P is located in one of the halfspaces it determines). A facet is a face of maximal degree

I tried showing that if there exists a vertex v such that this isn't a facet, then P is a convex hull of a finite set not containing v, which is a contradiction, but without success.

HOpe you'll be able to help me