The 39-year-old pop star is jetting to Cannes in the south of France to perform a short set for Anant Ambani and his bride Radhika Merchant.
A source told The Sun newspaper: "They have invited 800 guests who are currently on a space-themed cruise around Europe, with stops in Barcelona and Genoa".
"It will arrive in Cannes on Friday for the big bash, which will be at a £40 million estate".
"The party itself will only last five hours but Katy will headline it, with a DJ also being flown in as part of the top-tier entertainment".
"Afterwards, guests will watch a huge fireworks display from a small armada of ships waiting in the Bay of Cannes".
The loved-up couple will officially tie the knot in July, but they're determined to stage a memorable pre-wedding event".
The insider added: "When they say there's been no expense spared, they really mean it."
Meanwhile, The 39-year-old pop star is jetting to Cannes in the south of France to perform a short set for Anant Ambani and his bride Radhika Merchant.
A source told The Sun newspaper: "They have invited 800 guests who are currently on a space-themed cruise around Europe, with stops in Barcelona and Genoa.
"It will arrive in Cannes on Friday for the big bash, which will be at a £40 million estate.
"The party itself will only last five hours but Katy will headline it, with a DJ also being flown in as part of the top-tier entertainment.
"Afterwards, guests will watch a huge fireworks display from a small armada of ships waiting in the Bay of Cannes."
The loved-up couple will officially tie the knot in July, but they're determined to stage a memorable pre-wedding event.
The insider added: "When they say there's been no expense spared, they really mean it."
Meanwhile, Katy recently stepped down from her role on 'American Idol', and the pop singer called for a female star to replace her on the panel.
The 'California Gurls' hitmaker believes there should always be a female voice on the 'American Idol' panel.
Katy - who starred on the TV show alongside Lionel Richie and Luke Bryan - told E! News: "That would be too many men, let's be honest".
"But we love Jelly Roll, and I'd love for him to be on this show whenever it's appropriate."
Katy also stressed that her replacement needs to be someone who is "honest and bold, not scared of negative comments".
The chart-topping singer suggested that she's faced more scrutiny than her male co-stars.
Katy said: "When you have an opinion, when you're bold, when you're a female, it just happens."recently stepped down from her role on 'American Idol', and the pop singer called for a female star to replace her on the panel.
The 'California Gurls' hitmaker believes there should always be a female voice on the 'American Idol' panel.
Katy - who starred on the TV show alongside Lionel Richie and LukeBryan - told E! News: "That would be too many men, let's be honest".
"But we love Jelly Roll, and I'd love for him to be on this show whenever it's appropriate".
Katy also stressed that her replacement needs to be someone who is "honest and bold, not scared of negative comments".
The chart-topping singer suggested that she's faced more scrutiny than her male co-stars.
Katy said: "When you have an opinion, when you're bold, when you're a female, it just happens".