Keep ModelState After Redirect inside ExceptionFilterAttribute

Question

I have a Mediatr pipeline behaviour which handles validation as a cross cutting concern, using FluentValidation it throws a ValidationException containing the validation errors. This saves me having to have ModelState.IsValid on every action. (Lets ignore that it uses an exception for flow control at the moment, it's a trade off I can accept).

So now, if there is a validation error, I have a ValidationException to handle. I do not want to have try{}catch{} in all of my actions either, so I am creating an ExceptionFilterAttribute to handle the validation exception.

Currently it looks as shown below. I am grabbing the errors and merging them into the ModelState. I then somehow have to get back to the page to make use of the ModelState and show the errors nicely.

The only way I can see how to do that would be a RedirectToRouteResult but of course this will cause me to lose the ModelState.

Is there a way to maintain ModelState for the redirect or return to the page from here? So far I cannot see a way to do it.

    public class ValidationExceptionHandlerFilter : ExceptionFilterAttribute
    {
        public override void OnException(ExceptionContext context)
        {            
            if(context.Exception is ValidationException)
            {
                context.ExceptionHandled = true;
                ValidationException vEx = (ValidationException)context.Exception;
                ModelStateDictionary msd = new ModelStateDictionary();

                foreach (var err in vEx.Errors)
                {
                    msd.AddModelError(err.PropertyName, err.ErrorMessage);
                }

                context.ModelState.Merge(msd);

                context.Result = new RedirectToRouteResult(context.HttpContext.Request.Path);
            }

            base.OnException(context);
        }
    }

//edit

I have changed to using /ExceptionFilter rather than ExceptionFilterAttribute since its an expected exception, but the issue remains of how to maintain ModelState