The Duchess of Cambridge was pretty in purple as she attended the Goring Hotel's 105th birthday celebration in London today, but she's not the first pregnant star to have sported the flattering Erdem frock. Back in September 2012, Yahoo! CEO Marissa Mayer, then eight months into her first pregnancy, wore a similar  dress from the same Resort 2013 collection, which she had custom made by the London-based designer in honor of the San Francisco Symphony Opening Gala. Kate, 33, who is seven months pregnant, wore the £995 ($1,528) Darla design, which features three-quarter-length sleeves and ends just above the knees; while Marissa, 39, opted for a longer sleeveless variation which was better suited for evening wear. Scroll down for video . Maternity chic: The Duchess, 33, who is seven months pregnant, wore a £995 ($1,528) Erdem design, which features three-quarter-length sleeves (L), while Marissa Mayer, 39,  opted for a  sleeveless variation in 2012 (R) While Kate appears to have worn an off-the-rack version of dress, which is no longer available for purchase, Marissa was lucky enough to have been gifted a custom version in 2012. 'My friend and brilliant designer Erdem made me a maternity gown for the opening of the SF Symphony tonight,' the Wisconsin-born mother-of-one tweeted before the gala. Kate, who was pictured leaving the five-star London property at lunchtime today, wore her chestnut locks loose and teamed the dress with a pair of bespoke navy suede court shoes made by her favourite designer, Alexander McQueen, and a neat indigo clutch by Stuart Weitzman for Russell & Bromley. Stepping into spring: Kate appears to have worn an off-the-rack version of the dress (L), which is no longer available for purchase, from Erdem's 2013 Resort collection . Erdem Resort 2013 Darla dress in purple . Click to check out the current Erdem collection at Net-a-Porter! Visit site . Well this is a nice surprise. We weren't expecting to see the Duchess of Cambridge today but here she is looking fresh as a daisy in a lovely floral print frock as she stepped out of the Goring Hotel. This spring-ready dress is by Erdem and is from the London based designer's Resort 2013 collection. So not only is Kate rocking one of the coolest high end labels around but she's still wearing regular fitting clothes, despite being seven months pregnant. How does she do it? With fans in Alexa Chung, Kate Bosworth and Keira Knightley, Erdem is now a regular feature on the red carpet and Kate's look today confirms just how into fashion she is. Styled with her favorite navy blue suede Alexander McQueen heels and a clutch by Stuart Weitzman, she's the picture of elegance. And what you can't see is that the dress has a cute cut out at the back. Gorgeous! Unfortunately it is no longer available to buy but if you click the link (right) you can take a look at the current collection at Net-a-Porter. For those who want to steal Kate's style for less we've found some pretty prints that will do the trick. L.K. Bennett's 'Rosa' dress is a dead ringer for the Erdem original or check out Coast and Marks and Spencer for similar styles. If the Duchess is dressing for spring then we've all got the royal seal of approval. Coast Harla print dress . Visit site . Asos Maternity floral print dress (now reduced to $41.50) Visit site . Little Mistress floral print dress at Asos (now reduced to £56) Visit site . Sam & Lavi floral dress at Revolve . Visit site . Fond of purple: Marissa, pictured in February (R), had a version of Erdem's floor-length dress (L) custom made for her by the Canadian-born designer when she was eight months pregnant . Marissa, who is estimated to be worth more than $300million, opted for a small silver clutch and a set of statement earrings to accompany her maternity gown, and wore her blonde hair scraped up into a bun. The executive first revealed her pregnancy news on the very day Yahoo! announced her hiring, and gave birth to her son Macallister on September 30, 2012, with her lawyer husband Zachary Bogue present. Canadian-born British-Turkish fashion designer Erdem Moralıoğlu, is known for his romantic and imaginative designs, which range in price from £390 ($600) to more than £1,300 ($2,000). The label counts celebrity fans including Alexa Chung, Kate Bosworth and Keira Knightley, and has been a favourite of Kate's for some time. Indeed, the English rose was regularly photographed wearing Erdem's versatile designs while she was pregnant with Prince George, now one. Kate is due to give birth to her second child with Prince William, the Duke of Cambridge, in May.
The Duchess of Cambridge, 33, wore a £995 ($1,528) floral Erdem dress today in London, from the designer's 2013 Resort collection . Marissa Mayer, 39, wore a custom variation of the same dress to a San Francisco event in September 2012 .