Taylor Swift moved an audience in Arizona to tears on Monday when she performed a song she's only performed on one other occasion; , a 2012 track inspired by a mother's love for her four-year-old son who died from cancer.The song is based on a blog written by Maya Thompson, who is credited as a co-writer on the single. Maya was in the audience at Taylor's show on Monday, and so the singer took the opportunity to make a special dedication.

Taylor Swift gave a rare and emotional performance of in Arizona on Monday

"In my opinion, one of the bravest things that a human being could ever do is to go through something absolutely unbearable and then share their experience with the world. And I think the braver you are, the more brutally honest you are," Taylor told the crowd as she gently strummed on her guitar. "There's a woman here tonight named Maya Thompson," she continued. "And she has lived in this area and brought her kids up in this area. And I wouldn't know half as much as I know about childhood cancer and childhood cancer research if she hadn't shared her story about her son Ronan."

Taylor was visibly moved as she started to talk about Maya's blog, Rockstar Ronan. "I would read it every night," she said. "And in it was this account of what it's like to watch cancer take over your life. And since then, I've had cancer hit really close to me in my family." (The songstress revealed back in April that her mum Andrea has been diagnosed with the disease.)After asking the crowd to give Maya a round of applause, Taylor introduced her performance of , which she originally released as a charity single to help raise money for the Ronan Thompson Foundation and other cancer charities. The 25-year-old previously performed the song at a September 2012 Stand Up To Cancer telethon.

"I just wanted to take a moment to try and play this song," she said. "I can't promise that I will sing it well, or not get really emotional, but I'm gonna try… I think because Maya is here tonight - I think she deserves it."Maya later shared a short clip from Taylor's heartfelt speech on Instagram, writing: "I still can’t believe tonight. I still can't believe you did this. This will forever be one of the most special moments of my life. Thank you @taylorswift for your beautiful heart and for never forgetting my Ro. I love you to the moon and back."

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