Nokia Lumia 1520
The device shipped with Windows Phone 8 preinstalled and was upgradable to Windows Phone 8 . 1 Now this device is included on the Microsoft list of Windows 10 Mobile upgrade , it can be upgraded through the Windows Insider program too . 
<triplet> Windows Phone 8 <subj> Windows Phone 8.1 <obj> followed by <triplet> Windows Phone 8.1 <subj> Windows Phone 8 <obj> follows <subj> Windows 10 Mobile <obj> followed by <triplet> Windows 10 Mobile <subj> Windows Phone 8.1 <obj> follows <triplet> Windows Insider <subj> Windows 10 Mobile <obj> operating system