In 2004 Gold Coast mum-of-two, Kelly Rennie was 70kg, wore a size 14-16 and was crippled by daily panic attacks and reliant on antidepressants.

But when the enterprising 35-year-old transformed her body and created a fitness guide for busy mums like herself to trim down, she never imagined she would receive praise from a client as high-profile as Kate Middleton.

Incredibly, the Duchess used Kelly’s post-natal guide after giving birth to Prince George in 2012 and even sent Kelly and business partner Katie Bulmer-Cooke a letter expressing her thanks.

Now fitness model Kelly has signed and delivered Kate a signed copy of her latest book, hoping it will help her after the Duchess gives birth to her third child, due in April.

Kelly said: “To get the letter back from Kate showed us the program could work for any mum.

“It meant so much at the time. That routine was a post-natal program, whereas this one is a sustainable fitness routine for the months that follow.

“If Kate can do it with the first two, she can do it with the third.

“She just needs to keep the same principles she applied after her first two kids as she obviously has managed to look after herself well!”

Former finance worker Kelly was driven to turn her life around after the birth of her second child when she fell into dark days plagued by panic attacks, antidepressants and weight gain, which left her at 70kg.

It was then that she decided to battle her demons with fitness, taking up at-home exercise.

Within 18 months, the mother of two had shed 20kg and whipped herself into good enough shape to become a star in the world of fitness modelling.

Kelly said she boosted her metabolism by replacing her fast food and sweets habits with a diet of wholesome, nutrient-dense foods like chicken, vegetables and power shakes.

These days, Kelly cuts an inspiring figure — and it’s no surprise she has encouraged legions of mothers to get fit from home, in their own time.

Kelly, who now weighs 50kg and wears a size 10, said: “I had a stage of jumping from diet to diet, relying on dieting pills and antidepressants, and suffering from chronic panic attacks.

“I decided to get I had to beat that by myself, so I weened myself off medication and I decided to get out of that spot and dive into training.

“After I had my second child, I unfortunately became a single mum. That’s when I got my passion for helping mums.

“I think the most important thing is being realistic and sustainable. It’s a lifestyle approach they can do every day for the rest of their lives.

“Most mums are emotional eaters, so part of it is letting go of emotional eating. Having some chocolate or a glass of wine is fine, but not every day and not for the wrong reasons.”

Weight loss tips for busy mums

1. Be aware of stresses in your life

2. Let go of emotional eating and keep wholesome food in the house

3. Keep hydrated and cut coffee in favour of green tea

4. Start training by doing short sessions from home

5. Build a strong support network including family and friends

Kelly’s diet before

BREAKFAST: Cereal or toast.

LUNCH: Sandwich, crisps and a chocolate bar.

DINNER: Fast food takeaway such as McDonalds with an unhealthy dessert.

Kelly’s diet now

BREAKFAST: A ‘powershake’ made from almond milk, natural protein, berries, avocado and half a banana.

LUNCH: Salad with chicken, peppers, broccoli, carrots.

DINNER: Chicken stir fry with rice and lots of vegetables.