The chart-toppers have joined a line-up including Clean Bandit, Trevor Nelson, Alex James, dance group Diversity, BBC Two radio presenter Jo Whiley, and Sara Cox for the event onboard the cruise line’s newest ship Iona.
There will also be a special performance from P&O Cruises’ new brand ambassador Gary Barlow, and appearances from Strictly Come Dancing’s contestant Chris Ramsey, judge Motsi Mabuse and professionals Amy Dowden and Ben Jones.
Other entertainment includes a silent disco and aerial viewings in the SkyDome.
“We are breaking new ground on Iona, with some of today’s biggest music artists performing at Ionafest,” said Paul Ludlow, P&O Cruises’ president.
“This really is the festival of the year and I’m sure that our guests will be just as excited about these new line-up additions as we are.
“The backdrop of the Norwegian fjords will give guests a dramatic landscape to enjoy a variety of entertainment, incredible acts and mouth-watering pop-up restaurants, making this a truly once-in-a-lifetime opportunity.”
Ionafest will take place through the Norwegian fjords on a sailing between 4 and 11 July from Southampton, which starts at £749pp.