Only show RelatedProducts when necessary

Im trying to figure out how to show a certain html block when certain conditions are true.
However i get the following error:

Compiler Error Message: CS1061: 'Nop.Web.Models.Catalog.ProductDetailsModel' does not contain a definition for 'RelatedProducts' and no extension method 'RelatedProducts' accepting a first argument of type 'Nop.Web.Models.Catalog.ProductDetailsModel' could be found (are you missing a using directive or an assembly reference?)


  @if (Model.RelatedProducts.Count > 0)
  {
    <div class="combinations">
      <div class="wrapper">
        <h2>Combinations</h2>
        @Html.Action("RelatedProducts", "Product", new { productId = Model.Id })
      </div>
    </div>
  }


Above code is placed in ProductTemplate.Simple.html (and it is working without the if statement only then it will show the title even if there are no products.

Already figured it out.
I placed the title in the RelatedProducts.cshtml template.