Why is an explicit interface declaration needed here? (WITH#)

Question

I am trying to implement a very simple interface and use it to access a property of a type that is accessed directly through the interface:

interface ITest { IOther Other { get; } } interface IOther { } class Other : IOther { } class Test : ITest { public Other Other { get; set; } } 

However, I get the following build error:

 Error 13 'Test' does not implement interface member 'ITest.Other'. 'Charger.Shared.Test.Other' cannot implement 'ITest.Other' because it does not have the matching return type of 'IOther'. 

Now I understand what the error says, but I cannot understand why. Other implements IOther, so why the problem?

The wrong solution would be to explicitly implement the interface:

 class Test : ITest { public Other Other { get; set; } IOther ITest.Other { get { return this.Other; } } } 

Why is this template needed?

Thanks.

EDIT: Suppose in the actual custom code where I am having this problem, declaring Test as this is not an option:

 class Test : ITest { public IOther Other { get; set; } }