Warning: A SPOILER for Bridgerton season 1 is in the last paragraph.
Bridgerton’s most mysterious character, Lady Whistledown, is voiced by the incomparable Julie Andrews for a few important reasons. Lady Whistledown is the faceless narrator of Bridgerton. She appears to know everything that’s going on in everyone’s lives and is willing to publish every salacious detail, no matter who is involved. Her gossip column, Lady Whistledown’s Society Papers, is the constant talk of Bridgerton's high society in Regency Era London, but the column also functions as the narration for the show.
Julie Andrews’s easily recognizable voice, with her distinguished English accent and perfect diction, immediately paints a picture in the viewer's mind of who Lady Whistledown could be. Obviously, most viewers likely pictured Julie Andrews herself, but since it’s implied early in the show that Whistledown belongs to the inner circle of the Bridgertons and Featheringtons, the audience is led to believe that Whistledown is an older and especially dignified woman - possibly Lady Danbury. But while the audience is fooled by Julie Andrews’s voice, the Bridgerton cast of characters are fooled by her writing.
Lady Whistledown’s voice suits exactly what the characters believe her to be. Within the show, the two characters most obsessed with Lady Whistledown’s identity are Eloise Bridgerton and Queen Charlotte, but neither of them gets close to guessing the truth until the very end of the show. After Queen Charlotte and Eloise bond over their obsession and agree to help each other uncover the identity of the mysterious author, Eloise continues to gather clues and report back to the queen. Eloise finally narrows Lady Whistledown’s identity down by eliminating possibilities one by one.
Because Lady Whistledown knows every scandal in London, Eloise initially believes that Whistledown must be an older widow of high social status who attends all the most lavish parties but goes largely unnoticed by the other guests. When Lady Danbury laughs off Eloise’s accusation, Eloise moves on. Then, Eloise thinks it might be a maid or cook in her own household or possibly the Featheringtons. When it’s pointed out to Eloise that anyone in the working class would be too busy for such hobbies, Eloise thinks that it must be Madame Delacroix. Eloise and the queen are, of course, wrong on all counts.
Julie Andrews's voice represents the fact that Bridgerton’s audience and its characters have a specific and limited idea of who Lady Whistledown could be just from hearing her name and knowing what she writes. No one would ever have guessed the gossipmonger's real identity is none other than Penelope Featherington. Despite the fact Eloise is in close contact with the real Lady Whistledown throughout all of Bridgerton, she never suspects her best friend as she can’t imagine Lady Whistledown as anyone but an older, potentially lonely or bored woman. For starters, the bold and cheeky persona of Lady Whistledown is vastly different than Penny's awkwardly shy, earnest demeanor. It's also hard for the prim and proper London gentry to imagine a teenager having the impertinence (and wherewithal) to pull off such an endeavor. Having Julie Andrews as the voice of Lady Whistledown is the perfect bit of symbolism to show just how limited the views of Bridgerton's high society are.