https://www.theverge.com/2018/5/7/17326808/microsoft-cortana-update-alexa-integration-build-2018

Microsoft first announced its Alexa and Cortana integration last year, and the company is providing an update today. Despite falling behind both Google Assistant and Alexa, Microsoft’s Cortana will now include access to Amazon’s digital assistant. At Microsoft’s Build conference today, the software maker demonstrated Cortana running on Alexa and vice versa.

The integration works by simply summoning Cortana with the command “Alexa, open Cortana.” You can then ask follow-up questions or commands like “send an email” to a particular person that you wouldn’t normally be able to do with Alexa alone. Likewise, you can bring up Alexa within the Cortana interface on Windows 10 and get access the skills that Alexa offers.