Meghan Markle is attending royal Christmas and every firstborn knows what's going on here.

Meghan Markle has been invited to attend the British royal family’s Christmas this year.

At first, this statement doesn’t sound like a big deal since, you know, Prince Harry and the 36-year-old are ENGAGED and all.

But then I learned something that made me, a firstborn, shudder with barely suppressed (and wholly misplaced) rage. That is, Kate Middleton was not allowed to attend the royal Christmas when she was Prince William’s fiancée.

Kate had to wait until she was officially William’s wife and the Duchess of Cambridge to be given the right to sit down to a Christmas meal with her partner of almost a decade. 

Listen: We discuss Christmas traditions on Mamamia Out Loud:

At first, this might seem like a slight against Kate. Make no mistake. It’s not.

This is all about William and Harry. And it’s a common phenomenon every firstborn will recognise: the rules for the eldest child are different to the rules for the second child and subsequent siblings.

Strict rules your parents set out – in this case: no girlfriends at Christmas – are somehow relaxed by the time the second child reaches the same age or milestone, so that they either don’t apply or are so bent out of shape they might as well not exist.

And it happens all the time.

You, the eldest, had to wait until you were 14 to hang out at a shopping centre with your friends alone. Your little sister or brother was doing it at 12.

You argued and fought for your $2 a week allowance. A year later your two younger siblings were pocketing $5 each week.

You couldn’t go to a party with any alcohol until you were 18. Your younger siblings were given a six-pack when they were 16 and a half.

You begged and begged your mum to get your ears pierced and got them done on your sixth birthday. Your sister? She was wearing earrings at five.

You finally convince your parents you’re old enough for a phone at 15 and so they’re getting you one for Christmas. Your 13-year-old brother gets one AT THE SAME TIME.

There's no real explanation from your parents as to why the rules changed. At least, nothing they can offer that makes you feel as if this backflip isn't the greatest of the world's great injustices.

There are theories, of course, as to why this happens. Your parents are more relaxed with their second child, they've either realised they were too strict with you, or they're just too tired to care anymore. Either way, it does nothing to make you feel better about having to push really hard for something that your sibling waltzes in and gets given without even asking for it.

So to you, Prince William, we feel your pain. Please know that a million other firstborns are rolling their eyes right now too.