Hmmm ... interesting timing, Justin Bieber.

On Sunday, the 21-year-old took to Instagram and posted a throwback photo of himself and former flame Selena Gomez holding hands. This "crazy throwback," as he captioned it, just happened to come a day after Gomez was reportedly spotted making out with One Direction's Niall Horan .

Bieber and Gomez have a lengthy and tumultuous history. They first got together in 2010 and have broken up only to reconcile soon after so many times we've lost count. While the pair last broke things off in December 2014 , they've remained weirdly close as exes. It's not uncommon for friendly exes to grab an occasional meal together, but Bieber serenading the 23-year-old singer with a rendition of "My Girl" at a hotel bar ... that's something else.