The One Direction star took to his Instagram Stories to praise the US pop superstar for the ''important'' album-titled track.
Alongside a screenshot of the song, he wrote: ''This song is a classic and it's so important for music.''
And the 'Blank Space' hitmaker re-posted the message on her own Story, and wrote: ''THANK YOU NIALL!! (sic)''
The pair previously surprised fans at Taylor's Wembley Stadium show on her 'Reputation Tour' last year by performing a rendition of the Irish hunk's solo hit 'Slow Hands'.
The 25-year-old star isn't the only pop star to heap praise on Taylor's new music.
Kim Petras recently admitted she is ''thankful'' to Taylor for flying the flag for the LGBTQ+ community on 'You Need To Calm Down'.
The 29-year-old singer featured a number of stars from the community - including singer Hayley Kiyoko, YouTuber Hannah Hart, Olympic figure skater Adam Ripper, and 'RuPaul's Drag Race' star Todrick Hall - in her music video for the song, and said her decision to do so came as she wanted to be more vocal about her support for the community.
And transgender star Kim, 26, applauded the 'End Game' singer for being ''brave'' enough to use her huge platform to speak out to the large percentage of her fans who are straight.
She said: ''Taylor Swift's fan base is so mainstream and so middle America, where it's not as progressive as some other parts.
''It's great that she is spreading that message to her fans who maybe don't have gay friends.
''I am thankful to her for doing that as part of the LGBTQ community.''
Taylor recently admitted she feels she needs to do more for the LGBTQ+ community after a conversation she had which made her realise she hadn't been ''loud and clear'' about her position.
She said: ''Maybe a year or two ago, Todrick and I are in the car, and he asked me, 'What would you do if your son was gay?'
''The fact that he had to ask me ... shocked me and made me realise that I had not made my position clear enough or loud enough. [I told him] 'If my son was gay, he'd be gay. I don't understand the question.'
''If he was thinking that, I can't imagine what my fans in the LGBTQ community might be thinking. It was kind of devastating to realise that I hadn't been publicly clear about that.''
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