You might remember the fateful day model and reality TV star Kendall Jenner deleted her Instagram. Alas, it was just over a week ago. But on Monday, the 21-year-old returned, and now fans are saying they know exactly why she left.

Lip. Fillers.

Never underestimate the Internet’s fascination with an unsubstantiated theory.Never.

It all started when Kylie Jenner shared a photo on Twitter, ahead of a Facebook Live to promote her and Kendall’s new bookTime of the Twins.

But fans had little to no interest in the book. All they wanted to talk about was a certain set of lips.

Going live on my Facebook in a few minutes!! Just finishing up our interview with E! #TimeoftheTwins https://t.co/sTl7Nmum43 pic.twitter.com/L5YXMKPMLm

— Kylie Jenner (@KylieJenner) November 22, 2016

While some reactions were lighthearted, a number of fans appeared to be annoyed and even angry at Kendall for potentially undergoing the cosmetic procedure.

@KylieJenner wooaahh. Kendall seems having lip fillers of her own

— sammy⚠ (@jnsmnth) November 22, 2016

@KylieJenner ok Kenny with the lip fillers. I see you ????????

— Jennifer (@jennifer_sali) November 22, 2016

@KylieJenner pic.twitter.com/FB5UPUngkY

— Paola Salcedo-Prado (@paaowow_) November 22, 2016

@KylieJenner why did kendal get her lips done man

— Kristi Kline (@krazedkristi) November 22, 2016

Kylie used that “i overdraw my lips” line too when she first got her injections .. it’s okay @KendallJenner

— hym..✨ (@gvess_) November 22, 2016

nnn kendall thinks she’s slick deleting her social media when really she just got her face done again pic.twitter.com/tWvYgy5QHx

— k ???? (@arianaswhip) November 22, 2016

Ultimately, the widespread conversation prompted Kendall’s 19-year-old sister Kylie to defend her.

On Snapchat, the founder of Kylie Cosmetics attempted to diffuse the rumours. “You guys Kendall let me overline her lip today with lip liner and everyone thinks she got lip injections,” she said. “I’m sorry Kendall.”

Unsurprisingly, the comments about Kendall’s lips weren’t the only negative ones aimed at the Jenner sisters yesterday. Several fans accused them of being insensitive, given that their brother-in-law had been hospitalised just hours before their Facebook Live. Another popular criticism was that they hadn’t evenwrittenthe book, and didn’t even appear to know what it was about.

But it’s all in a days work when you’re part of the Kardashian-Jenner clan. I certainly don’t envy them.