Problem with redirect

Hi!
I have this problem. I launch this link:
[url]http://mysite/AA123a[/url]
My index.php file process this url and launch header(“Location: “. $file_path.”?id=”.$_REQUEST[‘id’]);
This is an html page and my browser link become become [url]http://mysite/temp/file.html[/url].
Instead what I want to do is to show the contents of the html file (file.html) but keep the same base url [url]http://mysite/AA123a[/url]

RewriteCond %{REQUEST_URI} ^{^(/.*?/.*?)/.*?$}
RewriteCond %{QUERY_STRING} ^{^id=([A-Z]{2}[0-9]+[a-z]}*)$
RewriteRule ^{^(/.*?)/%1} [R=301,L]

this is not correct..
Help please..

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