The "D" format specifier represents a custom date and time format string.
The format string is defined by culture's DateTimeFormatInfo.LongDatePattern property.
The custom format string is −
dddd, dd MMMM yyyy
Example
using System;
using System.Globalization;
class Demo {
static void Main() {
DateTime myDate = new DateTime(2018, 9, 20);
Console.WriteLine(myDate.ToString("D", CultureInfo.CreateSpecificCulture("en-US")));
}
}Output
Thursday, September 20, 2018