The websites of Hello!, Marie Claire, Elle and other magazines were awash with pictures of Britain's royal family and photos of and by Testino, 60, celebrated for his candid shots of musicians, fashion models, film stars and royalty.
Hello's coverage of the news was typical, featuring photos by Testino of Charlotte's parents, Prince William and his wife Kate, peppered with snaps of sports star David Beckham, model Kate Moss and actress Scarlett Johansson.
Marie Claire focused on the Peruvian photographer's friendship with William's mother, Princess Diana, saying his commission to photograph her granddaughter was a "touching tribute".
He also took the official engagement photos of William and Kate, which were turned into postage stamps.
"The Duke and Duchess are delighted that Mario Testino will help capture this important moment for their family and look forward to sharing the photographs with the public," a spokesman for the Cambridge's official residence Kensington Palace said.
Born on May 2, Charlotte is due to be christened on Sunday at St Mary Magdalene Church at the Queen's Sandringham estate in Norfolk, northeast of London.