When did Windows start accepting forward slash as a path separator?

[Stephen Ferg]

I have a question that is not directly Python-related.  But I thought
I'd ask the most erudite group that I know... :-)

When did Windows start accepting the forward slash as a path separator
character?

At one time, it was accepted as a truism that Windows (like MS-DOS)
was different from Unix because Windows used the backslash as the path
separator character, whereas Unix used the forward slash.

But now, among a small group of cognoscenti, it is a truism that this
is a myth, and that Windows will allow you to use either the forward
or the backward slash as a pathname separator.

I hypothesize that originally Windows accepted only the backslash, and
then at some time it changed to accept the forward slash as well. 
Does anyone know when that change occurred?  Was it with the
introduction of support for long filenames in NT and Win95?