She may be Duchess of Cambridge, but when it comes to bouncing back post-pregnancy, Kate Middleton is a queen!

Since giving birth to her third child, Louis, earlier this month, the 36-year-old is likely well on her way to her pre-baby weight. Back in 2013, Middleton credited The Fit Mummy Manual as her workout of choice after giving birth to baby George. LIVESTRONG.COM spoke exclusively to the program’s co-founder, Kelly Rennie of Busy Mum Fitness, who revealed just what it takes to complete the diet and fitness plan. “You’ve got to consider that you’ve had a baby in your belly for nine months, and it’s very crucial that you do things properly,” Rennie says for those looking to get back in shape.

Stay Hydrated

 Many new moms swear by coffee to keep them going, but Rennie advises her clients to cut it out completely and instead only drink water. “As a mom is breastfeeding, I tell her that she should be drinking three liters of water a day,” she says. “What happens is a lot of moms go to coffee. They skip their breakfast, they have a coffee, they’re dehydrating themselves, and one of the most important things we need in our body is water.” Rennie reveals that for new moms who are stressed, coffee causes much more harm than good. “A lot of moms are already living in an anxious world trying to deal with what’s going on, so why bring in a stimulant that may feed that?”