Four games into the 1989 NFL season, Mike Shanahan was fired by the Raiders after a 1-4 start.

Kyle Shanahan, who was in third grade at the time, came home to unexpectedly find his dad sitting on the couch. That’s when the Raiders’ rivalry became a big deal for the 49ers head coach.

“Well, it’s different ‘cause it changed throughout my whole life. It used to be huge, they fired my dad when I was in third grade,” Shanahan said.

“I’ve never come home from school and seen my dad sitting on the couch before, and I still remember that day coming home and he’s sitting on the couch on like a Wednesday.”

“I’m like, ‘What’s going on?’ That’s in third grade, so you take that personally.”

More than 30 years later, Shanahan and his squad took on the Raiders at Levi’s Stadium Sunday. San Francisco earned its seventh win of the season with a 38-17 victory.

Shanahan is the franchise’s record-holder for most games coached after he surpassed legendary 49ers head coach Bill Walsh last month.

And while Mike Shanahan’s tenure with the Raiders didn’t work out, he is a revered NFL head coach known for his revolutionary offensive design and back-to-back Super Bowl titles with the Broncos.

He is also a member of the Broncos Hall of Fame.

His son may one day surpass him and be enshrined in the Pro Football Hall of Fame. A singular Super Bowl titie will all but cement that.