The unlikely duo chatted up a storm as they rubbed shoulders at the WellChild benefit concert at the Royal Albert Hall in London.
Prince Harry has been a patron of the charity, which aims to support seriously ill children and their families, since 2007.
Lady Gaga lent her talent to the event, performing with crooner Tony Bennett at the benefit and praising the fantastic work of the charity.
The Born This Way singer told the royal: “We are so happy to be here tonight and be of any help, we think you are fantastic. And thank you for bringing it here so we can support you.”
Gaga dazzled in a sparkling silver dress with a plunging neckline showcasing her very impressive bust and of course she added matching diamante eyebrows. While her blonde locks were swept up into a retro beehive.
Although the 29-year-old pop star received some backlash for the cleavage-emphasising number she wore to meet the royal.
But considering she once donned a dress made entirely out of meat, this was reasonably tame for the quirky singer.
Meanwhile the talented Tony Bennett revealed to the 30-year-old prince that he had a friendship with Princess Diana: “Your mum was a good friend of mine. I did many benefits with her.”
Kensington Palace re-tweeted posts which were made by the very grateful charity and read: “Tony Bennett singing smile – not a dry eye in the house :).”
Before adding: “Lady Gaga on stage now praising the work of WellChild thank you @ladygaga.”
The charity raised almost $200,000 for sick children and its CEO released a statement thanking the stars for their contribution.
“WellChild is thrilled that Lady Gaga and Tony Bennett are supporting WellChild through this concert, the proceeds will be a massive boost to our work to support seriously ill children and their families across the UK,” the statement read.