The royal couple began their visit at Thompson Dock, one of the city's main tourist attractions and the last place that the Titanic stood on dry ground before her doomed maiden voyage in 1912.
The British bank said the figure, which is similar to estimates it gave for Taylor Swift's UK tour in 2024 and the Oasis UK reunion last year, highlighted "the rise of concert tourism".
The UN health agency has declared the surge of the highly contagious haemorrhagic fever an international health emergency and called an urgent meeting on the crisis.