Something else for a change: a challenge for the reader.

Given the following topology:

The router does not have any routing protocol configured. It does have all interfaces configured: towards the WAN cloud, towards the PC 2 subnet, and an IP address towards the PC 1 subnet. PC 2 is a Windows computer, static IP
PC 1 is a Windows computer set to DHCP client, but there is no DHCP pool configured on the router or any other device. PC 1 hasn’t had any special changes to the software settings or TCP/IP stack.

Now the question: under what circumstances will PC 1 and PC 2 be able to ping each other?

To my knowledge, this question has two possible solutions. You have an idea? Please share it in the comments!

Update: the solution.