The NHL broke new ground by doubling the size of the league and adding six new franchises for the 1967-68 season. Two of those teams -- the Flyers and Penguins -- are still around.
While the cross-state rivals didn't cross paths in the postseason until 1989, the Flyers and Penguins have been frequent combatants since.
"The fans always remind us how they hate the Penguins, and I'm not a big fan of them, either," said Claude Giroux.
First, let's take a quick trip down memory lane:
The Backup Plan, 1989
Trailing Mario Lemieux and a young Jaromir Jagr, the Flyers forced the heavily-favored Penguins to a Game 7 at the Igloo, only to discover starting goalie Ron Hextall was hurt and couldn't go. In stepped backup Ken Wregget. He stopped 39 shots against the team he'd later play for in the 4-1 series' finale. Then, the Flyers fell to Montreal (in six) in the conference finals.
Changing of the Guard, 1997
The first round featured emerging Flyers star Eric Lindros vs. Mario Lemieux, the Penguins' legend who had announced that he would retire after the playoffs.
"They were a lot better than us," recalled Jagr. "It was kind of emotional."
The Flyers made sure Mario wouldn't leave with a Prince of Wales Trophy and won in five. As he and Lindros embraced in the post-series handshake line, it seemed apparent the balance of power in the East had shifted. Or so we thought. That proved to be the height of the Lindros era.
Count 'em: Five overtimes, 2000
Jagr will never forget this series where the Penguins won twice here, then dropped the next four games. The epic Game 4 went until nearly 2:30 a.m. and lasted five OTs.
"We almost had the series. We would've been up 3-1 -- and all the sudden it put them back in the series,'' said Jagr. "Those wins and losses in overtime are mentally exhausting and we couldn't recover after that."
Changing of the Guard II, 2008
The Flyers had no answers for Sidney Crosby, Evgeni Malkin and the Penguins, who outscored them 20-7 and easily advanced to the Cup finals in five. But the series laid the foundation for the recent hatred.
"It's definitely amped up, with a lot of emotion," said Scott Hartnell, one of just four Flyers still around from that series. "There's a lot of body checking. A lot of everything."
Talbot silences Philly, 2009
Having battled back from a 3-0 hole to win the next two games, then surge to a 3-0 lead in Game 6, the Flyers had all the momentum. That's when Pittsburgh's Max Talbot -- after losing a fight to Dan Carcillo -- held his finger to his mouth to quiet the Philly fans. More than that, it inspired his teammates as they went on to score five unanswered goals and clinch the series.