I've found the answer to my problem guess it could be useful for others out there.
The problem was with the way i assigned new URLs to my Iframe, i used Jquery so it looked something like that:
$('#myIFrame').attr('src',newUrl);
When assigning the URL in that manner it adds a new entry to the browser's list of visited URLs to go back to.
That wasn't the desired behavior, so after some googling i found that you can assign a new URL to an Iframe object without adding it to the 'back-list', it looks like that:
var frame = $('#myIFrame')[0];
frame.contentWindow.location.replace(newUrl);
This way my back button behave exactly as expected.
btw, i got my answer from here.
Hope this was helpful to you as it was to me.
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