A spokesperson told Us Weekly magazine: "The Duke and Duchess of Cambridge met with Brad Pitt and Angelina Jolie Pitt at Kensington Palace on Friday afternoon.
"They discussed their shared interest in combatting the illegal wildlife trade."
The two couples will have no doubt been swapping parenting tips, with the Duke and Duchess's two-year-old son Prince George believed to be in attendance at the meeting.
Brad and Angelina - who have Maddox, 13, Pax, 11, Zahara, 10, Shiloh, nine, and six-year-old twins Knox and Vivienne - are also believed to have offered the royal couple a present for their newborn baby, Princess Charlotte.