News Kate Middleton Will Debut Her Baby Bump at This Public Event By Olivia Bahou Olivia Bahou Facebook Olivia Solomon is a New York-based writer and editor who covers all things fashion, lifestyle, celebrity, and pop culture. She was previously the Assistant Digital Editor for InStyle, and her work has appeared in many national publications. InStyle's editorial guidelines Updated on September 21, 2017 @ 10:30AM Pin Share Tweet Email Kate Middleton has been resting at home since announcing the news of her third pregnancy and the return of hyperemesis gravidarum, or extreme morning sickness. But according to Kensington Palace, the Duchess of Cambridge is set to make her first public appearance since announcing she’s expecting, and the event is sooner than you think. Middleton will step out alongside her husband, Prince William, and brother-in-law, Prince Harry, on Oct. 10 for cause near and dear to her heart: World Mental Health Day. The expectant royal will attend a reception at Buckingham Palace to “celebrate the contribution of those working in the mental health sector across the U.K.” Middleton has long been an advocate for erasing the stigma around mental health, even appearing in a video earlier this week on the topic. The clip, filmed back in January, is an instructional tool to help children be open about their feelings and mental health. Chris Jackson/Getty The duchess chose an elegant green Prada tea-length dress ($2,340; matchesfashion.com) with a high neck and long sleeves for a visit to Princess Diana's memorial garden with Princes William and Harry. Chris Jackson/Getty Prince William Says Princess Charlotte Is Bound to Be Trouble On Tuesday, Prince William hinted that royal baby No. 3 may be coming “sooner than you think,” so all eyes will surely be on the Duchess and her growing baby bump come Oct. 10. As for us, we’ll be taking bets as to what she’ll wear.