He tweeted an explanation and apology, writing: "Been sick all night. Still really unwell. Absolutely gutted!!. So sorry to let our fans down at NRJ. :( sorry :( hope the lads smash it !!"
Of course, fans were concerned, as #GetWellSoonLouis started trending on Twitter. Some of the 1D guys passed along well wishes to Louis and they carried on without him (sniffle), performing "Steal My Girl" and winning an award for International Duo/Group.
He tweeted later: "Thanks for all the lovely messages !! I've felt s**t all day but all the get well soon stuff is cool :) I just gotta get right for the final"
Not to worry though, as Louis made a speedy recovery to join the guys on The X Factor finale with the guys tonight. He tweeted: "Feeling better today ! So so excited for tonight ! @TheXFactor"
@NiallOfficial thanks Niall ! Can't wait to get into my own bed !! Hope it all went great !!- Louis Tomlinson (@Louis_Tomlinson) December 13, 2014
@zaynmalik thanks man . I had a shit day to be honest ! Wish I could have chilled with you boys- Louis Tomlinson (@Louis_Tomlinson) December 13, 2014
Feeling better today ! So so excited for tonight ! @TheXFactor- Louis Tomlinson (@Louis_Tomlinson) December 14, 2014