So, who were the starstruck ones?
Us Weekly reports that Kate and William took afternoon tea with Brad and Angelina in a private meeting at Kensington Palace on Friday.
Angelina is already well-known in royal circles, having been ennobled by the Queen for her work with survivors of sexual violence in war zones, and she was in London having flown in earlier in the week to attend a lunch at the Foreign & Commonwealth Office as part of that charitable effort.
Us weekly reported that the Royals were 'really excited' about the afternoon tea, and were joined by their son Prince George.
The Jolie-Pitts also brought a special gift for their daughter Princess Charlotte, Us reports.
"Everyone got on splendidly," a source told Us.
"Brad and Angelina spent much longer with the Duke and Duchess than planned. They ended up staying for almost a few hours."
The insider added: "They discussed their shared interest in combatting the illegal wildlife trade."
It was the first time meeting for the foursome. In 2014 they all attended the BAFTA awards but didn't cross paths.
In October 2014, Queen Elizabeth II made Jolie an Honorary Dame Commander at a private Buckingham Palace ceremony, which is the female equivalent of knighthood, for her humanitarian work.