Apple - Is it possible to use an Amazon Echo with HomeKit?

Philips Hue Bulbs are controlled by the Philips Hue Bridge or other ZigBee compatible bridge. HomeKit and Apple TV don't function as a true bridge or hub as it requires other hubs and bridges to connect to smart devices. The Apple TV simply gives you a remote connection from Apple TV to iOS over internet via iCloud.

Hue Bulb --(ZigBee)--> Hue Bridge --(LAN)--> HomeKit via Apple TV --(LAN/WAN)--> iOS device

Now, you can't use Amazon Echo with HomeKit, but this doesn't matter. Amazon uses Hue Bridge's built-in APIs to connect to Hue. Amazon and Hue can connect regardless of your HomeKit setup.

Hue Bulb --(ZigBee)--> Hue Bridge --(LAN/WAN)--> Amazon Echo

You can use both HomeKit and Amazon Echo (including Dot, Plus, Spot, and Show) in conjunction with HomeKit via iOS and Apple TV, provided you have the Hue Bridge as your controller.

My partner and I were looking at this this morning. She's just buying us a house and wants to go Smart Home.
The Echo Plus contains a built-in bridge that will talk directly to Hue, but can't (yet) do some of the higher functions like colour cycling.
So to add to @drivec's answer, it looks like this:

Hue bulb --(LAN)--> Amazon Echo Plus.

I don't know whether the cost of the Echo Plus (~£140) is better or worse than the cost of an Echo plus a Hub, but there's certainly less stages to the connection where something could go wrong. As to whether the same bulb can take commands from more than one source (the AppleTV and the Echo) I don't know.

And of course, trying to Google that gives me a much better answer: https://digitized.house/2016/08/idevices-bridges-apple-homekit-amazon-alexa-worlds/

Use the iDevices app. This allows you to talk to HomeKit via Alexa on an Echo.