Sony unveiled three high-end smartphones starting with the flagship Xperia Z5, mini variant Xperia Z5 Compact and the big phablet Xperia Z5 Premium at the IFA 2015 event. Meanwhile, a new report said that the “Sony Xperia Z5 Ultra” is silently gearing up for release.

The Xperia Z5 Premium, which is touted as the world's first smartphone with 4K screen resolution on board, is apparently not the only device to come with an Ultra HD display. While the new handset with “Premium” moniker was believed to be the “Ultra” handset, a new report by Price Pony said that the Sony Xperia Z5 Ultra is under development, and it is a huge phablet.

As far as the rumored Xperia Z5 Ultra specifications are concerned, the handset will apparently come with a gigantic 6.44-inch display, packed with a 4K resolution of 2,160 x 3,840 pixels. Similar to the flagship, Compact and Premium devices, this handset will also come with the same 23-megapixel rear-facing camera unit.

In addition, a powerful 4,000 mAh battery unit will reportedly help in keeping the lights on for a longer period of time. Under the hood, the phone will come powered by Qualcomm's upcoming Snapdragon 820 processor. This configuration will be aided by a solid 4 GB of RAM.

Meanwhile, the Sony Xperia Z5 Ultra release date has been reportedly set for March 2016. However, it is worth noting that, Sony has not confirmed the Xperia Z5 Ultra specifications so far.