Canon flash on a Nikon body?

Can you use a Canon 580 ex II on a Nikon D90 body?

Added (1). I just want to know if it works… A friend of mine has one and I'm curious if the brackets are the same.

Why would you want to?

for compatibility reasons, it is always best to use manufacturer with manufacturer, meaning Nikon flashes with Nikon cameras

The exact correct answer depends partly on the type of flash involved.

If it is an old-fashioned flash that has only one contact in the center of the foot,
it should work on any camera that has a hot shoe.

However, most modern flashes are "dedicated" to a specific brand of camera
because they have unique connections that enable through-the-lens metering
and other fancy functions. In this case, attaching a different brand of flash
can cause expensive-to-repair damage to circuitry in the camera.

Some companies, such as Vivitar and Sunpak,
make dedicated flashes for each brand of camera.

I have a Vivitar flash that can be separated into two parts:
the flash head and a module that makes it work with Pentax cameras.
If I wanted to use that flash with, say, a Nikon camera,
I would need to obtain a Nikon-type module for it.

Be very careful about this!

Its probable that the flash wouldn't even fire and its definite that there wouldn't be any communication between camera and flash. Usa the Canon flash on a Canon DSLR and use a NIkon flash on your