Co-worker bragged about lying on resume on social media, now what?

Scrolling through my newsfeed, I came across a meme that a co-worker was tagged in by a friend. In the comments, they admitted to lying on their resume to get their job and then a subsequent promotion... all the while joking and laughing and thinking it was funny.

I am one of a handful of other coworkers who are friends with this person on social media and could potentially have seen this post. This impacts me because the promotion they received was to be my replacement. I will train this person, and be their backup. How can I in good faith keep this to myself and take this person seriously moving forward?

What to do? And how to go about it?

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