Trying to create a child element in Xml serialization, doesn't show up

I am trying to generate the following XML, and this is also the first time that I ever serialize XML. Could anyone explain to me why my <issuer> element isn't showing up?

What is generated:

<samlp:Response xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion" ID="02279359-0581-41c7-a66b-199523ac8eab" IssueInstant="18:07:2014 10:41:37 AM" xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol" /> 

What I need generated:

<samlp:Response ID="02279359-0581-41c7-a66b-199523ac8eab" IssueInstant="18:07:2014 10:41:37 AM" xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol" >
    <saml:Issuer xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion">http://ift.tt/1yAVbNS;
</samlp:Response> 

What I don't understand is that I marked the Issuer as an XMLElement.

Here is my code.

MySaml.cs

[Serializable]
[XmlRoot(ElementName = "Response", Namespace = "urn:oasis:names:tc:SAML:2.0:protocol", IsNullable = false)]
public class MySaml
{
    [XmlAttribute("ID")]
    public string ID { get; set; }

    [XmlAttribute("Version")]
    public const string Version = "2.0";

    [XmlAttribute("IssueInstant")]
    public string IssueInstant { get; set; }

    [XmlAttribute("Destination")]
    public const string Destination = "http://ift.tt/1nijPjR";

    [XmlAttribute(Namespace = "xmlns", AttributeName = "samlp")]
    public const string samlp = "urn:oasis:names:tc:SAML:2.0:protocol";

    [XmlElement(Namespace = "urn:oasis:names:tc:SAML:2.0:assertion", ElementName = "Issuer", IsNullable = false)]
    public readonly Issuer Issuer = new Issuer();

}

Issuer.cs

[Serializable]
public class Issuer
{
    [XmlText]
    public const string Text = "http://ift.tt/1yAVetb";

    [XmlAttribute(Namespace = "xmlns", AttributeName = "saml")]
    public const string saml = "urn:oasis:names:tc:SAML:2.0:assertion";
}

Lastly, The methods I am trying to use to generate the SAML (and pardon the ugly string manipulation there - I am planning to bomb it)

protected void Page_Load(object sender, EventArgs e)
{
    GenerateSamlAssertion();  
}

private void GenerateSamlAssertion()
{
    var response = new MySaml();
    response.ID = Guid.NewGuid().ToString();
    response.IssueInstant = DateTime.UtcNow.ToString("dd:MM:yyyy hh:mm:ss tt");

    SerializeXml(response);
}

public XmlDocument SerializeXml(MySaml mySaml)
{
    var xmlSerializerNameSpace = new XmlSerializerNamespaces();
    xmlSerializerNameSpace.Add("samlp", "urn:oasis:names:tc:SAML:2.0:protocol");
    xmlSerializerNameSpace.Add("saml", "urn:oasis:names:tc:SAML:2.0:assertion");
    var serializer = new XmlSerializer(typeof(MySaml));

    using (var writer = new StringWriter())
    {
        try
        {
            serializer.Serialize(writer, mySaml, xmlSerializerNameSpace);             
            var doc = new XmlDocument();
            doc.LoadXml(writer.ToString().Remove(0, writer.ToString().IndexOf("\r\n") + 1));
            return doc;
        }
        finally
        {
            writer.Close();
        }
    }
}

I know what I am missing must either be something stupid or something small.

Thanks in Advance :)