The Irish singer is currently enjoying some time off following 1D's mammoth world tour but rather than sit at home relaxing he was in the X Factor audience on Saturday night (16 November) for the latest performance show.
Niall – who finished in third place with One Direction in 2010 - tweeted throughout his time at the studio, mostly to tell the performers how great he thought they'd done.
He tweeted to Tamera Foster: "Big fan! Great job tonight honey!" Similar tweets went to Rough Copy and Nicholas McDonald.
The highlight of Niall's evening, however, appears to have been gorgeous X Factor judge Nicole Scherzinger!
"No doubt about it! @NicoleScherzy is my favourite person ever ! She is hilarious on this show ! @TheXFactor," he wrote.
Niall was back again for the results show the following night, which saw Miley Cyrus and X Factor judge Gary Barlow performing.
Although some viewers expressed disappointment in Miley's toned down performance, Niall was clearly impressed. "Sick @MileyCyrus was incredible tonight, what a voice."
He also told fans that despite now being a global megastar with millions of album sales under his belt, going back to X Factor was as nervewracking as it had been when he was just starting out.
"It was great to be back home @TheXFactor today! Love that place! Seeing all the crew and contestants and dermot ! So nerve wrecking though. (sic)"
Fans will see Niall and the 1D boys back on the X Factor stage next week when they join in the show's ten-year anniversary celebrations.
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