Kourtney Kardashian's son Mason Disick joining Instagram has fans saying the same thing

Kourtney Kardashian's son has just made his Instagram debut, and most fans of the celebrity family are saying the same thing.

Reality TV youngster Mason Disick officially joined social media on Saturday (25 May) and accumulated 369,000 followers within a matter of minutes.

Mason was only a baby when he made his debut in the spotlight. (Marcel Thomas/Getty)

If you're anything like me and can barely keep up with which of the multitude of Kardashian-Jenner kids belongs to which multi-millionaire parent, don't worry, we're here to give you a quick refresher.

The Insta-newbie, aged 14, is the firstborn child of Kourtney Kardashian, 45 - who also happens to be the eldest of the iconic K-J brood - and her ex-husband Scott Disick, whom she dated between 2006 and 2015.

As well as Mason, the big-name couple also welcomed a daughter named Penelope, 11, and another son, Reign, nine, before finally ending their relationship following several on-off stints.

Fan-favourite socialite Scott, now 41, would often appear on his wife's family's hit series Keeping Up With The Kardashians, along with their three children.

Mason celebrated his social media move at the weekend with a photo alongside his little brother. (Instagram/@masondisick)

Though the Disick children were barely out of nappies when they appeared on the legendary late Noughties show, fans of the family have followed their on and off-screen antics ever since.

Featuring infrequently on the latest rendition of the show, Hulu's The Kardashians, Mason, Penelope and Reign regularly have viewers in stitches with their hilariously sassy and quick-witted remarks.

What many fans of the original Kardashian series may not realise, however, is exactly how much the eldest of the family's children have grown up during their time in the spotlight.

So much so, that a horde of followers have been left absolutely mind-blown this week after realising that eldest child Mason is actually a teenager.

After the 14-year-old set himself up with an Instagram account at the weekend - sharing his first three snaps - fans couldn't contain their shock at his milestone.

Mason made his Instagram debut at the weekend. (Instagram/@masondisick)

"Wdym Mason Disick has an IG page, I watched his birth. We’re getting old!" one fan tweeted.

Another went on: "Mason Disick is now on Instagram - yes, we’re all old asf."

"I'm old asf bc WHYYYY does Mason Disick have an instagram acc," a third said in shock.

"Mason Disick joining Instagram, I'm so old," claimed another.

Apparently, however, it isn't just Mason's fans that have been left gagged at the prospect of the former TV baby joining social media.

Commenting on her nephew's first pic, Kim Kardashian, 43, wrote at the weekend: "I can’t believe this is happening."

Khloe Kardashian, 39, added: "You’re really on Instagram"

Topics: The Kardashians, Keeping Up With The Kardashians, Kourtney Kardashian, Celebrity, TV And Film, Reality TV