How int is the backing type for enum

Question

According to this post int is the backing type for enum.

When I check the source code of .NET System.Enum abstract class inherits from System.ValueType abstract class.

But when I check the System.Int32 struct it inherits from interfaces but not from System.ValueType.

On the contrary, when I decompile mscorlib.dll and check the Int32 struct it says that the struct has base type of System.ValueType.

But still checking the decompiled source code I can not see anything about System.ValueType.

It makes me think that the struct keyword makes the declaration auto-Sytem.ValueType, which Microsoft also denotes in this reference.

But I still have a question. As far as I know, inheritance of two different classes from the same parent does not imply that one also inherits from other. I mean if B:A and C:A this does not always mean that C:B.

Also, when I check the source code, System.Enum has quite a different implementation to that of System.Int32.

So, under these circumstances, how does this fit with 'System.Int32' being the backing type for System.Enum?

Can anyone explain?