The Australian rapper was playing a sold-out concert at the O2 Shepherd's Bush Empire when Rita surprised the crowd by walking on stage.
Her entrance was met with cheers and screams and the two pop stars then launched into a rendition of their single 'Black Widow'.
When the track was done, Rita, 23, couldn't stop gushing about Iggy, saying: ''This girl is the truth, I'm telling you that London. She's got a heart of gold.''
During Iggy's hour-long set she performed her hit singles 'Fancy', 'Bounce' and 'Work', while gyrating with her four female backing dancers, all of whom were dressed in skimpy monochrome leotards.
The 24-year-old star almost suffered an injury when she slipped soon after she arrived on stage.
While performing her opening track 'F**k Love', she stumbled on the second floor of the double-levelled stage but luckily managed to save herself from falling to the ground.
After the incident, she joked: ''I only just escaped my own death up here on stage!''
It's not the first time the 'Change Your Life' singer has taken a tumble on stage. Last month, at a benefit concert before the MTV Video Music Awards (VMAs), Iggy fell off the stage when she was performing with Charli XCX, but luckily she emerged from her tumble unscathed.
We help you decide who to give your money to.
Nature-inspired songs we just can't get enough of.
Artists are coming up with different ways to entertain and help out this year.
Put these British films about music at the top of your watch list.
The Mifo O5 PROs are some of the most durable wireless earbuds on the market and we can't recommend them enough.
These songs were written for times like these.
Live musicians take a financial hit during the worst health crisis of a generation.
The sins of London have followed them home. After throwing Owen Shaw (Luke Evans) out...
The cast of 'Furious 7' talk about their favourite moments from the 'Fast & Furious'...