Run a new application every time VNC remote session is created by a user

Question

VNC is basically share the remote desktop of the host. I want to open a specific application whenever the VNC session is created to a remote host .There is xstartup script which is used to achieve this. But the problem here is , this script is referred at the first time when the "vncserver" command is executed not every time whenever the session is created from the vnc client. Please let me know , how to achieve this.