Taking her aside for a brief post-show interview at Swansea's Singleton Park, the BBC host said: 'I think you need to have a shower now,' in an apparent reference to the muggy conditions.
Luckily the pop star managed to see the funny side, quipping: 'I agree, I'm not offended, there's a lot going on and almost none of it's good.'
One penned: 'People need to stop creating problems, the whole Greg James shower comment was a joke, it was crazy humid today, plus performing, Taylor didn't even take offence.'
Another wrote: 'Taylor and Greg James have done interviews and stuff before and she obviously wasn't taken aback or offended by his joke can ya'll relax.'
Moments earlier, Taylor, 28, had wowed the 26,000-strong audience with a live performance of a string of hits from her 2017 album Reputation.
The star admitted to feeling 'a bit nervous' before her performance, telling Greg: 'We pretty much had no time to rehearse for this. This was kind of like, on the fly.'