[SalesForce] Display email template markup in VF without tags

I'm trying to include email template preview inside custom VF page, I've visualforce email template with messaging:htmlEmailBody only without plain text version.

I created custom VF to get email preview from controller and display it in this page. but body column is empty, I got markup of the email but when I try to display it display tags. not like preview from email template page inside force.com . I put it inside apex:inputTextarea with richText and readonly. I have button to insert lead and reRender template preview. but I got this error when I click on that button.

Rerender is not currently supported with rich text editing enabled 

So what I need is to display the email template preview with markup (Styled).

Email Template

<messaging:emailTemplate subject="Welcome Partner" 
                         recipientType="Lead" 
                         relatedToType="partner__c" 
                         replyTo="{!relatedTo.ReplyTo_address__c}">
    <messaging:htmlEmailBody >
        <p>Dear {!recipient.firstname},</p>

        <h2 style="color:#009DDC;">Welcome {!relatedTo.Company__c}</h2>

        <p><strong><i>This is sample:</i></strong> You received email!</p>

        <p>Regards,</p>
    </messaging:htmlEmailBody>
</messaging:emailTemplate>

VF page

<apex:page showHeader="false" controller="emailctrl" >
  <!-- Begin Default Content REMOVE THIS -->
  <apex:form id="theform" >
  <apex:pageBlock >
      <apex:pageBlockSection >
          <apex:inputField required="true" label="First Name" value="{!l.firstname}"/>
          <apex:inputField label="Last Name" value="{!l.lastname}"/>
          <apex:inputField label="Email" value="{!l.email}"/>
          <apex:inputField label="Company" value="{!l.company}"/>
          <apex:commandButton value="Preview" action="{!preview}" reRender="previewform"/>
      </apex:pageBlockSection>
  </apex:pageBlock>

  </apex:form>

  <apex:form id="previewform">
      <apex:inputTextarea readonly="false" value="{!et.markup}" richText="true"/>
  </apex:form>
  <!-- End Default Content REMOVE THIS -->
</apex:page>

Apex Class

public with sharing class emailctrl {
    public lead l{set;get;}
    public EmailTemplate et;

    public EmailTemplate getEt(){

        et = [SELECT id,body,Markup,HtmlValue
              FROM EmailTemplate 
              WHERE DeveloperName = 'welcome_partner'];
        return et;
    }

    public void preview(){
        // do nothing
    }
}