Kourtney Kardashian is seen in a flashback bikini photo from 25 years ago

Kourtney Kardashian has an incredible bikini body thanks to daily workouts in her home gym with a personal trainer.

And the Keeping Up With The Kardashians star proved this weekend she has always been in top shape.

To celebrate her 41st birthday, the mother-of-three was seen in a flashback photo from 25 years ago when she posed in a black-and-white two piece.

The petite wonder seemed to be at her hotel while on vacation in Hawaii.

The college graduate had her dark hair worn short and partially pulled back. There was heavy eye makeup on for the portrait as well as frosty beige lipstick.

Her arms were up on the balcony rail as she seemed to be impressed with her deep tan as she wore a black and white striped suit.

The POOSH founder’s body looks great, but she actually may look even better now.

Also this weekend, her supermodel sister Kendall Jenner shared a recent shot from a bikini modeling session.

Kourtney was in a black and beige leopard print suit with her hair in a turban – she was showing off a more muscular frame with abs and sculpted legs.

Her little sister was in something similar as she squatted down.

And there was another image of Kourtney in a purple bikini shared by Kim; the era seemed to be about 10 years ago. 

Kim shared a gushing 41st birthday tribute to her sister Kourtney.

The 39-year-old reality TV icon fired up her Instagram to post a string of throwback snaps of the pair of them together.

‘Happy Birthday @kourtneykardashian I had to find some good throwbacks to celebrate you today! I remember these moments so vividly,’ wrote Kim.

‘I love your strong will to do whatever makes your soul happy, the love you have for you children and for being the best big sister,’ she gushed.

‘I couldn’t be more thankful for our memories together. You pack a mean punch I love you so much and can’t wait until this is all over so we can celebrate together.’

Kim and Kourtney are the eldest two children of Kris Jenner and her first husband, the late O.J. Simpson lawyer Robert Kardashian.

The throwback snaps Kim posted on Saturday included not just Kim and Kourtney, but in some cases their sister Khloe and their mother as well.

A couple of sweet childhood pictures showed Kim and Kourtney together such as one where they were dressed up in matching striped shirts.

One picture was a solo shot of Kourtney who showed off her bombshell beach body in a barely-there purple bikini. 

Meanwhile the two sisters were seen having a vicious physical brawl on an episode of Keeping Up With The Kardashians last month. 

The catalyst was when Kim belittled Kourtney’s work ethic as well as that of their supermodel half-sister Kendall Jenner.

Kim bragged that ‘If I were on my deathbed, I would still show up’ to work and included Khloe in her praise.

However she sneered that Kendall would just ‘get anxiety,’ leading the model to insist: ‘I work my f***ing a** off when I’m sick or not.’

Kim then rounded on Kourtney who snapped: ‘You act like I don’t do s***. You have this narrative in your mind…I will literally f*** you up if you mention it again.’

The two stood up in a bottle-flinging slap-fight that was only broken up when Khloe physically planted herself in between them.

‘We actually had to shut down production for a week after that, because everyone was just so shook,’ Kim revealed on The View this week.

‘And so it was so uncharacteristic of us to really act like that. My mom saw that clip and was crying, and was just – she couldn’t believe that we were acting like that.’