Dear Samantha Markle: Here's what you clearly don't understand about being a sister.

When I was 15, I put my 13-year-old sister in the bath.

Well, by “put” I mean pushed. You know, hard enough to make her wail and cry. Why did I do such a thing? Because she criticised my “bacne” (for those of you playing along at home, that’s back-acne… acne of the back) while we were getting ready for a party together.

“Don’t mention Michelle’s bacne” was essentially a family rule from when I was 14 to 17. Mum enforced this with an iron fist and yet Evelyn blatantly disobeyed it to my own freaking face/back. While Mum was nowhere to be seen. It was all very calculated.

Anyway, she ended up bruised in the bath and I ended up grounded until approximately last Wednesday.

I also recall a fun incident where my elder sister and I got into a fist fight over a pair of netball training shorts. She said they were hers, but I swear to this day that they were mine. Needless to say, we ended up battling to the death for them on the top of the stairs, Greco Roman Wrestling style (the 2008 Beijing Olympics was on at the time and we felt inspired). Maybe this is my imagination taking over but I’m pretty sure Claire dangled my body off the edge of the landing, held a knife to my throat and forced me to surrender the shorts forevermore.

At this point I should clarify that 10 years on Evelyn, Claire and I are adults and the best of friends. The best. Seriously. If I could live with my sisters in a ginormous house with an endless supply of Maltesers and dogs, that would be heaven. I might even suggest it when I finish writing this.

We got through the whole “I hate you and will try everything to ruin your life” phase of our teenage years, and arrived at a place of love, brunch and brutal honesty.

Those who have sisters will relate. The bond is unique and unbreakable. There’s a level of transparency and loyalty that other relationships don’t and can’t have. Your sister might annoy the living bejesus out of you, but despite all her flaws and quirks, you are her fiercest protector and number one fan.

As a sister, even when things are rocky you have three jobs: To always have her back. To always want the best for her. To make her a cup of tea when she’s sad.

You tend to her like you would a plant; you water her when she’s droopy, you pop her in the sunlight, you give her the energy she needs to be strong and beautiful and alive.

That’s it.

LISTEN: In case you missed it, Meghan Markle has brought slut strands back. Yep the horrible, 90s hairdo is back, and all because of Meghan Markle. Post continues after audio.

Unless, it seems, you’re Samantha Markle. Then it’s your job to smear your sister’s name as much as humanly possible, all while making a quick buck.

In case you missed it – and you’re lucky if you did – Samantha, 53, is the half-sister of the soon to be royal, and has left no stone unturned in her plight to muddy Meghan’s spotless reputation. Because they share the same father, you see, Samantha is releasing a “tell all” memoir about Meghan’s secrets. It’s reported the working title for her book is ‘The Diary of Princess Pushy’s Sister.’ Charming.

Then, on Monday night, Samantha appeared on Channel Nine’s A Current Affair to do an interview about, well, Meghan again. You know, despite them not seeing each other since 2008.

“Honestly, what she could spend [financially] in a weekend would greatly help dad, so that should be a priority,” Samantha told the program about their bankrupt father. “I think you need to step up to the plate and make sure he is well taken care of.”

This was all voiced out of a pure concern for their father's wellbeing, of course. Not of wanting publicity and to $ell more book$ off the back of the sister she hasn't spoken to in years, or anything. (For the record, Tom Markle is said to be thrilled about his younger daughter's upcoming wedding; he's walking her down the aisle.)

Samantha then continued to explain how she was sad when Meghan divorced her ex-husband Trevor Engelson, because, “I really liked him though and admired him so much."

... Cool. I wonder why that wedding invitation hasn't arrived in the mail yet.

No matter what happened between Meghan and Samantha, no matter who shattered their clearly broken relationship, one thing here is evident: In writing that stupid book and giving these ludicrous interviews about nothing, Samantha is not being a sister. Samantha's being a bully.

Because no matter how bad things get, no matter how much you want to strangle each other on the staircase or push each other into a bath tub, you don't betray your sister.

And you don't try to block the sunlight from shining onto her plant just because yours is in the shade.