The 'What Makes You Beautiful' hitmaker admits he finds it tough to recall his band's lyrics as there is ''a lot of stuff to remember'' from that time.
He said: ''There's a lot of stuff to remember and I'm not as good at remembering as I used to be. There's been a lot of life that's happened since those songs.''
Speaking on Instagram Live, he added: ''Did we sing that in the final? I know we sang it at Judges' Houses. I think you sing it in the final, do you not? I'm sure you sing your first song in the final on X Factor.
''I should know, I've been on twice. I only made the final once. Did we even make the final if we came third? I don't know.''
And Liam still finds the band's meteorological rise to fame as ''insane''.
She said: ''It's insane, it really is. I still can't believe, I still feel like I don't know what the hell I'm doing. It's amazing and everyone's had such great success. It's been great hearing a lot of Harry's stuff at the moment.
'''Adore You', I see it in the charts all the time. I think he's really found his sound at the moment which is a joy to watch.''
And Liam previously said that if the band decide to reunite in the future, it would be likely they'd all perform one another's solo songs.
He said: ''For me the only way One Direction could better themselves from going to playing stadiums - like where else do you play? - is to manage to be, you know, like 'The Avengers', like we're successful on our own. Like if Iron Man wants to go and deal with someone, he just deals with them. He doesn't call up Hulk and be like 'oh, whatever' unless he really needs him. So my thing is, why aren't we like that? Like, we should go and boss it on our own and then when we do the show it can be like 'yeah, yeah, just sit down there boys, I'll sing a bit of 'Slow Hands'', you know what I mean? Imagine that?''
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