The actress and the European royal both looked stunning as they giggled while posing upon arrival at the gathering inside the Beverly Wilshire Four Seasons Hotel in California. The 38-year-old star looked petite as ever in a botanic print green and blue Oscar de la Renta frock, with Manolo Blahnik shoes, and a Charlotte Olympia clutch.
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Meanwhile the princess – who is a former Olympic swimming champion - towered over Reese in nude high heels. Both blondes were joined by Rizzoli & Isles actress Angie Harmon at one point, who donned a pink and blue dress, with her brunette locks pulled back into a high ponytail.
They were honouring Princess Charlene with the Champion of Children Award for her work with charities. One of those includes her own Princess Charlene of Monaco Foundation, which teaches water safety. The organisation additionally teaches strong sports values in youngsters through initiatives like the Learn to Swim programme.
Reese, 38, was last seen helping her pal Kate Hudson celebrate her 35th birthday at the weekend. She is a patron of the charity helmed by Princess Charlene. Demi Moore and Nicole Richie were all at a star-studded party on Saturday which was a joint bash for Kate and friend Jen Meyer.
Held in the Los Angeles’ No Name Bar, fashion editor Derek Blasberg posted several snaps on his Instagram account, including one that showed Kate and Jen, who is married to Tobey Maguire, blowing out their birthday candles.
Earlier in the night he also posted a picture of Reese, Jen and actress Jessica Capshaw with friends, writing next to it: "Reese, Jessica, Kelly, Jen and Emily: Blondes. Having more fun. Happy birthday!"