Fincantieri built the ship at their Monfalcone yard, where it was launched August 16, 2012. Measuring 142, 714 grt it is slightly smaller than Queen Mary 2's 148,528, but exceeds it in passenger capacity, with 3600 vs QM2's 2620. It is also slightly shorter at 1083 ft vs. 1132, but considerably broader. Depending on how you measure it, Royal Princess is 155 ft. at its widest - at the "sea walk", and 126 ft. at the waterline. By comparison QM2 is 135 ft. wide.
Both ships are part of the Carnival plc family, but operating under different brands. Princess Cruise Lines for the Royal Princess and Cunard for the Queen Mary 2.
The quest for ever larger cruise ships shows no sign of letting up, with Carnival building two sisters, to be named Regal Princess and Britannia - but they are far from the largest ships contemplated.