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UFC fighter Michelle Waterson had to choke back tears talking about Nick Santonastasso ... an amazing disabled athlete who's helping Michelle get ready for the biggest fight of her life.

Michelle is gearing up to fight Joanna Jedrzejczyk in October ... and says a recent encounter with Nick is giving her that motivational boost she needs to prepare.

FYI, Nick was born with Hanhart syndrome, an extremely rare condition that left him without legs and only one arm. Despite the circumstances, Nick has become an international bodybuilding sensation ... the dude is an absolute BEAST in the gym!

So, when Michelle saw Nick at a recent Tony Robbins seminar, she says his story left her with a new perspective on life.

Ya gotta hear Michelle tell the story ... she gets emotional. It's moving stuff.

Plus, we also spoke with Michelle's adorable daughter about the upcoming Joanna fight ... and why she thinks Waterson will be the UFC's first-ever Mom Champ!!