This belongs in a history book.

Unless you've been hiding under a rock the past week, you know that this is 23-time Olympic gold medalist Michael Phelps. At 31 years of age, Phelps is the most dominant male swimmer of all time.

Phelps also enjoys a good celebratory fist pump.

Clive Rose / Getty Images

And this is Katie Ledecky. Though she's only 19, Ledecky has smashed several world records, and has captured five Olympic gold medals in the process.

Like Phelps, she too enjoys a good fist pump.

Al Bello / Getty Images

There's no arguing that these two are among the best American athletes alive right now (and TBH the two might also be part mermaid). But what if I told you these two go way back, even before the 2012 London Olympics, which were Ledecky's first and Phelps' fourth?

Tom Pennington / Getty Images

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