htaccess集成了一个新参数

I am working on updating a friends site, and he has an htaccess file that looks like this:

<IfModule mod_rewrite.c>
Options +FollowSymlinks

RewriteEngine on

RewriteBase /WWI

RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ index.php?path=$1 [QSA,L,NC]
</IfModule>

Correct me if I am wrong because im still learning htaccess (wich is also why im here). But this code in combination with this php code determines wich page content needs to be loaded:

if(isset($_GET['path']) ){
    $cPagina = $_GET['path'] . '.php';
} else {
    $cPagina = 'indexContent.php';
}

include("partials/$cPagina");

So this is how the URL's look now:

www.development.dev/WWI/products/products_product

Wich just represents:

www.development.dev/WWI/products/products_product.php

This is accessed by:

< a href="/WWI/products/products_product" >

This construction, maybe outdated. But works fine.

So now this is the situation:

index.php?path=/WWI/producten/product_individueel&productid=3

And he wants to get this masked to:

www.development.dev/WWI/products/product/3

He also wants to keep as close to the current construction as possible, so I have tried this:

RewriteRule ^(.*)$ index.php?path=$1&product=$2 [QSA,L,NC]

So if I vardump the $_GET it returns this:

array (size=2)
  'path'    => string 'products/products_product' (length=29)
  'product' => string '' (length=0)

How can I put for example the '3' inside that 'product' whilst the URL seems like products/product/3

However this let me realise how less I know about htaccess and it peaked my interest. So I got searching and reading tutorials on how this works etc. But I did not once encounter a problem where the path is saved in combination with a second parameter.

I hope the info I gave is enough, and I also hope this does not seem like I am not trying, but after 2 days fiddling arround with htaccess and reading manuals etc. I just thought, lets try stack overflow.

Thanks in advance