Win10+Win7 dual boot issue

Dear all,

I hope I have not missed a thread with a similar problem:
I had Win10 installed on drive C: with the boot loader on drive D: (where I previously had my old Win10 installation). I wanted to add Win7 to my PC and formated drive D: - I totally forgot that I had the boot loader on that disk... Now I have Win7 on drive D: and drive C: is unchanged but I can not boot into Win10. I tried all the bootrec /fixmbr stuff, but found that my drive C: is not a MBR but a GPT...
Is there a way to access my Win10 installation without reinstalling the whole thing?

Thanks in advance!

What drive letter is your Windows 10 partition getting in Windows 7? Let's say it is D:\. Open an elevated ("run as administrator") command prompt in Windows 7. In the elevated command prompt Window run:

BCDBOOT D:\Windows /d /addlast

The path in red will be to the Windows folder on the Windows 10 drive letter.

Then reboot the computer.

The BCDBOOT D:\Windows /d /addlast command did not work in win7, but BCDBOOT D:\Windows did the trick - now the boot manager of Win10 is active and i can choose both OS! Thanks a lot!