Tyra Banks wants to ''change the world's perceptions'' of beauty.

The 45-year-old model has come out of retirement from the modelling industry to pose in a yellow bikini on the cover of the 2019 Sports Illustrated Swimsuit Issue, which marked her return to the magazine after being the first African-American model to pose on the cover alone in 1997 after being a joint cover star with Valeria Mazza in 1996.

And now, Tyra - who has changed her modelling name to BanX - has taken to her Instagram to reveal that she celebrates her more curvy figure and wants to ''re-define beauty'' to help make a ''difference'' in the industry.

She wrote: ''Remember the 10 year challenge every one was doing on social? The one where you posted a photo of yourself now next to a photo of yourself 10 years ago?

''Well, I guess this is my @si_swimsuit 22 year challenge. Scroll the pic to see. But to me, it's not just about what I'm looking like. It's about what I'm FEELING like. Back then, I knew I had a plan to do more than model. I knew I wanted to make a difference. I knew I had a calling to do more than for just myself. I just didn't know HOW I was gonna do it.

''Today, 22 years later, I rise out of bed everyday to show that yes, a woman who was a model (and is now a model again!) can indeed be powerful beyond pictures. Can indeed be a strong leader in changing the world's perceptions of narrowly defined beauty. Can indeed be an example for others to follow so I can sit back one day when I'm old and grey to enjoy the things that YOU are doing to push my mission further than I ever dreamed possible. Yeah, my 22 year challenge has a whole 'nother meaning beyond what you just SEE. #BanX (sic)''

Tyra - who is covering the iconic issue for the third time in her long career - was photographed by Laretta Houston in the Bahamas, and the former Victoria's Secret Angel admitted that she thought she needed to ''drop 30 pounds'' when she knew she was going to be on front of the magazine, but instead ate ice cream and is happy maintaining a healthy lifestyle.

She added: ''I thought I needed to drop 30 pounds. I thought I had to look the same. Then the ice cream called my name. Yep, all flavors. From Butter Pecan to Matcha to Coffee. I love me some ice cream and I just couldn't say no to it when I heard it calling. 'TyTy, Come eat me...' from my mom's freezer.

''So, this is me in @si_swimsuit today. Ice Screaming from mountain tops, 'Screw cookie cutter beauty!' Yes, we should exercise. Stay healthy. Take our vitamins. But sometimes we can give ourselves permission to work out with a scoop of frozen deliciousness in our hands. #BanX (sic)''