Host asp.net framework application in asp.net core web site

I have two applications, one built using asp.net core and one using asp.net framework. I am hosting both within IIS. One runs under an app pool setup as managed and one as unmanaged, as shown here:

As asp.net core application need to be setup as a web site (rather than an application within a web site) each application is setup as a web site, meaning both have their own port.

This is fine, except only one can be setup with port 443.

I want both to be accessible under 443, so I want to setup the .net framework application as an app under the .net core website (you'd normally setup .net framework apps under default website for example).

This is my setup (both running under port 888 for the sake of this example):

The .net core application runs fine, as expected:

But the .net framework app isn't running as expected and I get the following message:

HTTP Error 502.5 - Process Failure - The application process failed to start.

Has anyone achieved this or know what I'm doing wrong?
Thanks for tips in advance!

NOTE: Event log says:
Failed to start process with commandline '"dotnet" .\Core1.dll', ErrorCode = '0x80004005'.