Kim Kardashian opens up about some of the cruel things that her older sister Kourtney used to say about her  in high school on this week’s The Kardashians.

The 44-year-old Kourtney and 43-year-old Kim – who Donald Trump called the most overrated celebrity – are just coming off a bitter feud from last season that they have resolved in Season 4.

The family all gathered at a Bowlero bowling alley to celebrate Kourtney’s 44th birthday, when Kim revealed some painful insults Kourtney used in high school.

Early in the episode, others arrive at the party like Simon Huck, Corey Gamble, Malika Haqq and Kim Kardashian, who gives Kourtney a birthday hug, asking Kourtney to open her card as she gives Simon a hug.

Kourtney reads, ‘I’m proud to call you my sister. Hopefully this makes up for all the other things I’ve called you,’ as Kim shows the front of the card to the camera, adding, ‘Is this not so fitting or what?’

Opening up: Kim Kardashian opens up about some of the cruel things that her older sister Kourtney used to say about her in high school on this week’s The Kardashians

Bitter feud: The 44-year-old Kourtney and 43-year-old Kim are just coming off a bitter feud from last season that they have resolved in Season 4

Big saggy: Kim added, ‘Or like in high school she would say, “Ew my sister has big saggy t**s, you would hate her!” And like guys at school that I would like at a party and I’d literally walk away crying and be like, “Bye guys”‘

Kim adds, ‘I wasn’t sure if she’d be mad at me for this card,’ but Kourtney insists, ‘No!’ as Kim adds in confession, ‘One of my obsessions is looking for funny cards online.’

‘This one was made for me and Kourtney,’ Kim said in a joint confession with Kourtney, who adds, ‘We all used to say the meanest things. I used to have no feelings. All I would say is like, “You’re so f***ing cellulite-y!’

Kim added, ‘Or like in high school she would say, “Ew my sister has big saggy t**s, you would hate her!” And like guys at school that I would like at a party and I’d literally walk away crying and be like, “Bye guys.”’

Kourtney turns to her sister and says, ‘Well, I’m sorry for the past,’ as Kim says, ‘Thank you’ quietly with a hand to her heart.

The episode begins at Bowlero bowling alley, where Kourtney arrives with her son Reign and many others, to celebrate her 44th birthday.

Her mother Kris arrives along with grandmother MJ as they all wish her a happy birthday, along with her stylist Chloe Degadillo, as Kourtney is seen wearing a “Birhday Girl’ tiara.

‘I am turning 44. The 40s are the best, honestly. So many amazing things have happened to me in my 40s and I am so grateful,’ Kourtney says in confession.

Khloe Kardashian arrives and takes a photo with her older sister, with Khloe adding, ‘I wanna label this “Filthy Rich Cattle Drive.”’

Kourtney Kardashian laughs about teasing Kim in high-school

Sorry: Kim added, ‘Or like in high school she would say, “Ew my sister has big saggy t**s, you would hate her!” And like guys at school that I would like at a party and I’d literally walk away crying and be like, “Bye guys”‘

High school Kourtney: Kourtney Kardashian at 14 years of age

‘I can’t wait ‘till Khloe can join me in the 40s next year,’ Kourtney adds in confession, as Kourtney asks Khloe if they should, ‘do something vibier’ as Khloe picks her sister up and spins her around.

‘Khloe, put me down,’ Kourtney says, and when Khloe asks why, Kourtney says, ‘Cause… I’m very fragile,’ as Khloe complies.

While Kourtney doesn’t say why she is ‘fragile,’ the preview for next week’s episode shows Kourtney’s now-infamous pregnancy reveal back in June.

Kourtney was at one of her husband Travis Barker’s Blink-182 concerts when she held up a sign revealing she was pregnant.