Displaying alert from an action
It's a bad idea to modify the session state from inside a view or a partial view. Instead, I would create an alert view model

public class AlertViewModel
{
    public AlertType AlertType { get; set; }
    public string Message { get; set; }
}

public enum AlertType
{
    None,
    Success,
    Error
}


and use that from inside the view/partial view, for example:

@if (Model.AlertType != AlertType.None)
{
    string alertClass = Model.AlertType.ToString().ToLowerInvariant();

    &lt;text&gt;
        &lt;div class="alert alert-@alertClass"&gt;@Model.Message&lt;/div&gt;
    &lt;/text&gt;
}


This way, you avoid modifying the session where someone else may not expect it, and you have a cleaner view.

About populating the view: I do not know why you are using the session, but if the value is only needed for one request, you should consider using TempData instead. In any way, just populate the view model in the controller and remove the session value if you need to.