Modal popup display during browse back buttton

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C#

ASP.NET

C#4.0

In my web application i got 2 pages say page1 and page 2. Page1 contains a modal popup extender which shows some messages. When i click a button in page1 it shows modal popup and will redirect to page2. From page2 when i click browser back button it first shows my modal popup message. Here i dont want to show my modalpopup,i just want to go to page1. How can i do that. i tried by putting " modalpopupextender1.hide() " in pageload,but not working.