Refer to the exhibits.

The host 10.200.3.1 sends a TCP SYN packet on port 10443 to 10.200.1.10, which is the external IP address of the VIP object named VIP in Exhibit B1. The VIP object maps the external IP address and port to the internal IP address and port of the server 10.0.1.10 and 443, respectively1. The VIP object also enables NAT, which means that the source address of the packet will be translated to the IP address of the outgoing interface2.

The firewall policy ID 1 in Exhibit B allows traffic from WAN (port1) to LAN (port3) with the destination address of VIP and the service of HTTPS1. The policy also enables NAT, which means that the source address of the packet will be translated to the IP address of the outgoing interface2.

Therefore, after FortiGate forwards the packet to the destination, the source address, destination address, and destination port of the packet will be 10.200.3.1, 10.0.1.10, and 443, respectively.

You can find more information about VIP objects and firewall policies in the Fortinet Documentation