Just ask the most famous members of both fan groups.
Celebrity supporters took to social media to root for their teams on Championship Sunday. Some even showed up on the sidelines at Arrowhead and Levi's Stadium. It must've been nice to soak in the conference-clinching moments in person.
Honorable mention: Rob Lowe
The former 'Parks and Rec' star didn't want to pick sides. He was just rooting for a good game. Hence, a completely neutral NFL cap. How Chris Traeger of him.
10. Klay Thompson
Nothing shows your fandom quite like dropping a new team anthem right before the NFC Championship Game. Warning: The Bay Area native's track might get stuck in your head.
8. Henry Cavill
It's a bird. It's a plane. It's... former Superman actor Henry Cavill rocking his Chiefs gear like a Kansas Citian would. Bonus points should be awarded because Cavill grew up watching the other football in England.
7. TECH N9NE
6. Erik Karlsson and Timo Meier
So what if they play a different contact sport? San Jose Sharks players Erik Karlsson and Timo Meier sure can get behind their neighbors in Santa Clara. The defenceman and right winger had themselves a day at Levi's Stadium long before the Niners took the field.
5. Melissa Etheridge
4. Rob Riggle
Riggle brought all the energy he can muster to comedies like 'Step Brothers.' But a Chiefs AFC title win is the one thing that can tucker this former Marine out.
3. Brad Pitt
One of Hollywood's biggest stars couldn't make the Chiefs game back home in Missouri. So, one fan tossed Pitt an AFC Champions hat on the red carpet at the SAG Awards. Watch his face light up. That's a real fan for you.
2. Jerry Rice
The G.O.A.T. is football-famous, not actor or musician-famous. But the 57-year-old legend belongs on this list merely for his pregame spring at Levi's. Rice could start in Super Bowl LIV if his Niners really needed him.
1. Paul Rudd and Eric Stonestreet