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Lizzo says "Truth Hurts" ... but, in this case it certainly shouldn't for her -- 'cause the truth is she looked fantastic at a New York Fashion Week event Friday night!

cThe singer-songwriter hit up the Christian Siriano fashion show in the Big Apple ... flaunting her recent weight loss in a brown corset top and tight black skirt -- and, kicking up her leg with a huge grin on her face. Getty

Her hair is a dark red here ... parted on either side of her face and cascading down to her waist while she smizes for the cameras.

While Lizzo's weight loss may seem like old news at this point, it's clear she's still reveling in it ... posting a new clip just an hour ago in which she shared videos of her progress over the years.

The new clip -- set to Lizzo's recently releas

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