Nginx – Getting “real” IP in Nginx behind AWS network load balancer

I have a network load balancer which is forwarding traffic to an Nginx docker container running in ECS (using awsvpc network mode). My nginx config is as follows:

user  nginx;
worker_processes  1;

error_log  /var/log/nginx/error.log info;
pid        /var/run/nginx.pid;


events {
    worker_connections  1024;
}


http {
    server {

        allow all;
        listen 443 default ssl;
        ssl_certificate /etc/nginx/ssl/cert.pem;
        ssl_certificate_key /etc/nginx/ssl/privkey.pem;
        ssl_trusted_certificate /etc/nginx/ssl/chain.pem;

        ssl_prefer_server_ciphers on;
        ssl_protocols TLSv1.2;

        add_header Strict-Transport-Security "max-age=31536000";
        access_log /var/log/nginx/access.log;

        location / {
            proxy_pass http://blahblahblah;
            proxy_set_header Host $host;
            proxy_set_header X-Forwarded-For $remote_addr, $proxy_add_x_forwarded_for;
        }
    }
}

However when looking at the logs the X-Forwarded-For header doesn't contain the client's "real" IP, it just contains a series of internal IPs (one of which is the network load balancer's internal IP).

My understanding of the Network Load Balancer was that the client's "real" IP was supposed to be preserved as the incoming IP, why is is not showing in this header?