'I was sworn to secrecy!' Martha Stewart tried on her daughter's bikinis for Sports Illustrated

Martha Stewart was "sworn to secrecy" over her Sports Illustrated cover shoot.

The 81-year-old businesswoman - who has 57-year-old daughter Alexis with ex-husband Andrew - became the oldest person in history to feature on the cover of the iconic magazine's annual swimsuit this month and explained she had to keep quiet about the shoot so ended up roping her daughter to help her try on various bikinis.

She told ExtraTV: "We were sworn to secrecy, so I couldn't really talk about it to anybody. I asked my daughter Alexis. She said, 'Cool, cool,' and she gave me some of her old bathing suits to try on, so that was good."

The TV star went on reflect that becoming the oldest person to grace the cover means she has been able to "break barriers" and wants to encourage other women to reconsider life in the hope that it will help them believe that they can "look good" whatever their age.

She added: "It is breaking barriers and also encouraging other women to just rethink what they're doing. I think that is really going to help a lot, and it's also: you can look good at any age, you can feel good at any age, you should live well at any age. I think about living successfully, not aging well."

Martha also explained that she cut carbs in order to prepare for the shoot and ended up getting "sort of addicted" to Pilates and is also a keen hiker as she strives for fitness.

She added: "Did my Pilates this morning. I do it three days a week... I got sort of addicted to it. I Iike it a lot, but I also have to do my horseback riding and the other nice things… hiking."