'Best Song Ever' singer Niall looked very dapper in a smart suit as he attended a glitzy reception at the palace on Tuesday night (25 March).
And, where were his 1D bandmates, we hear you ask? Well, last night's event was to celebrate the contribution made by Irish people in Britain, hence the reason for Mullingar-born Niall being among the guests.
Niall, 20, was snapped shaking hands with The Queen during the evening and described the event as "mind-blowing".
"It's an absolute honour to be here with two great countries coming together - I couldn't believe it when I got the invitation," he told BBC. "To have met Her Majesty again was a great experience
One Direction met The Queen back in 2012 after performing at The Royal Variety Show.
Niall later tweeted: "I would to thank @BritishMonarchy and of course Queen Elizabeth for her invite to Buckingham palace yesterday evening."
There's no doubt Niall and One Direction have certainly made an impact in Britain (and across the entire world!) since forming on The X Factor back in 2010.
Niall was joined by several other famous Irish faces at Buckingham Palace including X Factor judge Louis Walsh.
A spokesperson for The Queen said: ""It was a really fun evening - great company and extremely relaxed. Her Majesty seemed to enjoy the craic."
Hopefully Niall didn't have too much craic, however, as he was up bright and early this morning at a rehearsal studio with his One Direction bandmates.
Earlier this week, the 1D boys were seen filming a new music video in Somerset.
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Watch One Direction's video for 'Midnight Memories' below: