Special interaction: Battle for Freljord

I just had a game as Ashe support, and enemy had Sejuani support. When I had 1 kill and 19 assists (20 total k+a), this interaction showed up (I fed). I knew this existed, but I've never seen it in action before.

Anyway, the game ended before either of us could kill each other. Such a shame.

Also, have anyone else seen this before?