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.

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.

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?

Just look at this amazing photo of Ledecky getting Phelps' autograph a decade ago when she was a wee nine-year-old swimmer. I'm guessing the photographer didn't know that they were shooting not one but TWO of the greatest American athletes of all time.
10 years ago: A 9-year-old named Katie Ledecky gets an autograph from Michael Phelps (Credit: Ledecky Family)