Problem using Virtualbox and VMWare while running Hyper-V

On Hyper-V installed Windows, Virtualbox only run 32bit OS and VMWare is cannot be used. Because on Hyper-V the OS you using is the first virtual machine on the Hypervisor. From: In other words, only booting to Windows with Hyper-V means run the first VM with it. So other Hypervisor cannot be used.