After Cassie shared her engagement, a message from a personal trainer landed in her inbox.

Earlier this month, on the eve of their 10 year anniversary, Cassie Young’s boyfriend proposed.

A radio host in the US, Cassie was quickly flooded with messages of congratulations from her friends, family and colleagues.

But there was one message Cassie couldn’t ignore, from a personal trainer who had offered up his services to help her “get in shape” for big day.

While the bride-to-be had no problem with his original offer, things quickly went downhill when she declined his help.

“I know you want to look the best on your wedding day,” the trainer – who hasn’t been named – responded.

“If you don’t hire me hire someone. Those pictures last for centuries. Your children’s children’s children will still have those pictures.”

Cassie replied that she would look her best “because I’ll be so happy I get to marry the man I love” before telling the trainer it has taken her a long time to love and accept her body.

"I'm constantly shamed or reminded that I'm heavy and I should be embarrassed," she wrote.

"I've battled past all that and like myself and how I look.

"The idea of me being embarrassed by my wedding pictures because I might be "fat" in them and people centuries from now will be ridiculing me? That's the insinuation and I say f*** that noise!"

But the trainer wasn't interested in hearing Cassie's body-positive message, telling her she was "lying to herself".

"You can accept how you look but you can't be happy with the way you look," he wrote.

"I just wish the whole big body acceptance people would accept the fact that they are not happy with their bodies."

He added that people only feel "fat shamed" because they have "something to be ashamed of".

Cassie responded that she was "sad" that the trainer's self-worth was "wrapped up" in his looks, and shared screen-shots of the entire conversation on Facebook.

UNAPOLOGETIC. This is the most revealing bikini I've EVER owned that I talked about on @TheBertShow the other day. I promised I'd post a #SuitYourself pic in it, and as I was picking these, I already started apologizing in my head for the flaws I knew people would be judging me for...the ones I was highlighting in my head (Am I too absurdly serious? Why is my face like that? I'm so burned! Who do I think I am with those poses, Ashley Graham? Oh God, look at that...) and then I decided IDGAF. I don't HAVE these superficial beauty flaws people arbitrarily decide are problems. # This is MY body and I'll be damned if I'll apologize for it. This body has carried me through 31 years on this planet - it's gotten me through hope and heartache, through near death sickness and great health, triumphs and failures. It's taken me to places around the world, has taken me on adventures big and small, and has been my HOME for my entire life. # For some of you, your bodies literally grew LIFE. For others, your bodies have carried you through marathons (running AND pizza bingeing AND Netflix). Our bodies have loved, have lost, have helped others, have let us feel total happiness and held strong through grief, and have been there every step of the way. They're the only thing we're born with and that we can say is truly OURS. Every curve, line, scar, freckle - it tells a story of a life filled with richness. Why are we so ashamed of them for not looking some specific homogenous way that some randos decided was "good." What a bunch of bulls***t. It's exhausting and I'm over it. # Here I am, in my unfiltered, I photoshopped, unedited jigglypuff glory and you can take it or you can #effyourbodystandards because I'm not playing that game anymore. I'm living my life to the fullest and I'm thankful that my body is taking my mind along for the ride. # #SuitYourself #BodyPositivity #PassThePizza #loveitorleaveit #lovethyself #unapologetic #effyourbeautystandards #nofilter #beachhairdontcare #sunburned #gingerprobs #swimsuitsforall

A post shared by Cassie Young (@cassandrayoung) on Jul 7, 2017 at 8:03am PDT

"I want every woman and man to know that it does not MATTER what you look like," she wrote.

"You are worthy. Love is out there for you. Life is waiting with open arms. It doesn't matter if you’re skinny or fat or between the two or willowy or broad shouldered or peer shaped or like a board or anything in between.

"You get good stuff in life by being YOU. That's what matters."

LISTEN: Mamamia Out Loud's Jessie Stephens shares how she felt body-shamed by her own gym.

Read about the body positive Instagram account you need in your feed, click here.

To read more from Jessica Clark, click here.