Return updated temp file back after watermark added.

I have a script that uploads files uploaded through my website directly to my Amazon s3 bucket.
This never saves the file permanetly to my server, just as a temp_file_location
This works perfect alone.

However,
I am trying to now add a watermark to the image before passing the temp_file_location to the s3 function to upload.

My question is, how can I use the code below, with the temp_file and then return a new temp_file (which is the watermarked version)

Here is just the code for the watermarker, I need this to start with the temp_file and leave me with a new temp_file_location:
 

$temp_file_name = $_FILES['theFile']['tmp_name'];
$image = $temp_file_name;
 
// creating png image of watermark
$watermark = imagecreatefrompng('watermark.png');  

// getting dimensions of watermark image
$watermark_width = imagesx($watermark);
$watermark_height = imagesy($watermark);
 
// creting jpg from original image
$image = imagecreatefromjpeg($temp_file_name);
//something went wrong
if ($image === false) {
    return false;
}
// getting the dimensions of original image
$size = getimagesize($image_path);
// placing the watermark 5px from bottom and right
$dest_x = $size[0] - $watermark_width - 10;
$dest_y = $size[1] - $watermark_height - 10;
// blending the images together
imagealphablending($image, true);
imagealphablending($watermark, true);

// creating the new image
imagecopy($image, $watermark, $dest_x, $dest_y, 0, 0, $watermark_width, $watermark_height);

//HERE I NEED A $temp_file_name TO BE THE UPDATED FILE WITH THE WATERMARK TO PASS TO THE S3 FUNCTION.


// destroying and freeing memory
imagedestroy($image);
imagedestroy($watermark);
 

Any ideas??
Thanks ahead!!