How to terminate SSH tunnel background process

I open an SSH tunnel (for port forwarding) from Windows 10 PC to a remote Linux server by typing the following command in Windows Command Prompt (substitute the actual DNS for host_IPv4_public_DNS):

C:> ssh -i thekey.pem -N -f -L 8888:localhost:8888 host_IPv4_public_DNS

After executing this command the tunnel opens, it is fully functional. The issue is that I don't get the windows command prompt (C:>) back. The process keeps running. How do I terminate this process/tunnel?