Update: A Nintendo UK representative has confirmed the device is real, saying:
We can confirm that Nintendo does plan to release the attachment but that any further announcements on the attachment will be made at some later time by Nintendo.
The rumours of a second analogue stick add-on for Nintendo 3DS continue to strengthen, with the device apparently spotted in this week's Famitsu magazine.
According to Siliconera, the peripheral takes the form of a clip-on cradle for the console, and adds a second analogue stick as well as R2 and L2 buttons, replacing the original R1 too.
The pages also appear to confirm the recent rumblings of Monster Hunter Tri G on 3DS, with series producer Ryuji Tsujimoto apparently calling the device a "secret weapon" for the console.
Nintendo's big pre-Tokyo Games Show conference is next week, so we'll finally know the truth then. In the meantime, what do you make of this rumour?