A rock solid CVG source at GDC in San Francisco has told us that not only does PS3's motion controller have a nunchuck add-on - but that it connects wirelessly to the main device.
Our source corroborated a previous post on NeoGAF, which revealed that the nunchuck features an analogue stick, with X and O button beneath it, and a d-pad below. On the underside of the unit are L1 and L2 triggers.
However, the wireless connection info is new - and another differentiation between Sony's device and Nintendo's similar Wii Remote controller.
Frustratingly, no brand name appears on the peripheral - so we can't yet confirm or rubbish claims that the peripheral will be called 'Arc'.
CVG's source had seen and handled the device - but hadn't yet used it in action.
We're expecting full details tonight from Sony's announcement at GDC (midnight GMT).