How do I have Siri read my WhatsApp messages to me?

The recent WhatsApp update allows Siri to read my messages out loud, how do I use this feature?

WhatsApp Messenger version 2.17.20 lets you ask Siri to read your messages out loud. All you need is iOS 10.3, have Allow "Hey Siri" turned on in Settings -> Siri and give Siri access to WhatsApp in Settings -> Siri -> App Support. If you have all of this set, simply say, "Hey Siri, read my last WhatsApp message."

How to have Siri read your WhatsApp messages out loud.