No matter which team wins Super Bowl XLVII, history has already been made with John Harbaugh, head coach of the Baltimore Ravens, and Jim Harbaugh, head coach of the San Francisco 49ers, becoming the first siblings in history to face each other at the big show.
Though the siblings themselves downplay the rivalry and emphasize the closeness, the nature of their relationship adds an additional dramatic undercurrent to the most anticipated sporting event of the year.
They're not the only siblings in sports history to face each other on the field -- or court or pitch, depending on the sport.
The most famous sibling rivalry in NFL history has to be between the New York Giants' Eli Manning and the Denver Broncos' Peyton Manning.
Although their teams have never faced each other at the Super Bowl, both brothers have managed to claim victories in the big game, earning Super Bowl MVP honors with each appearance.
Eli has one extra Super Bowl ring over his older brother, but Peyton's stats suggest he's the better quarterback.
While the Manning rivalry might be the greatest between brothers in sports, it's hard to find a more competitive pair of sisters than Venus and Serena Williams.
Although they will compete side-by-side in doubles tournaments, in singles tennis, it's every Williams for herself. Serena currently has the edge in head-to-head matches, with a 13-10 advantage over Venus, and has more Grand Slam titles to her credit as well.
Joe Dimaggio is a ballplayer whose name continues to resonate with fans decades after he left the sport. His brothers Dom and Vince might not have the same recognition as their eldest brother, but they were no slouches. All three were All Stars several times, though only Joe could claim three MVP awards and nine World Series championships.
In any sport, no sibling rivalry is more fast and furious than that of Michael and Ralf Schumacher, Formula One drivers who over the course of three years finished five races in the 1-2 spots.
The brothers' competitive relationship occasionally manifested itself in public, such as when the two had a war of words in the press following the 2005 Monaco Grand Prix.
Both drivers are now retired from Formula One racing.
While twins Tiki and Ronde Barber have achieved different degrees of fame in the NFL, one brother, Ronde, has been working steadily since he's been drafted and even won a Super Bowl ring. The other, Tiki, retired early from what would become a championship team at the peak of his career, started a second career as a broadcaster, became mired in scandal and then made a failed attempt to return to the NFL one month shy of his 36th birthday. So it's kind of a no-brainer who had the more successful athletic career between the two.
The Barber brothers aren't the only twins to make their mark on football. New York Jets head coach Rex Ryan and his twin brother Rob Ryan, a defensive coordinator for the Dallas Cowboys until his contract was recently terminated, both got their start in the family business joining the defensive coaching staff of their father, Buddy Ryan, when he became head coach of the Arizona Cardinals in 1994.
Considering that Vladimir and Vitali Klitschko are elite boxers that dominate heavyweight division titles in their sport, you'd think that these two fighters would be primed for a clash.
Though both brothers are fiercely competitive separately, they refuse to fight one another, likely a disappointment for fans but probably a point of pride among family.
A competitive duo with a third brother who might one day be an NBA prospect, Pau and Marc Gasol are All Star professional basketball players from Spain. Although they shared silver medals when Spain came in second to the United States in basketball at the 2012 Olympics in London, so far only Pau has managed to be on two championship NBA teams.
Staal brothersCorbis Images
Having a pair of siblings compete with one another in sports at a professional level is rare as it is. But the Staal brothers -- only two of whom appear in this photo since one photo of them on the ice could never include all of them -- are a foursome that play for different professional teams.
The Carolina Hurricanes in 2003 drafted Eric, the oldest of the Staal brothers. Next in line, Marc was picked up in by the New York Rangers. The Pittburgh Penguins brought Jordan onto their roster 2006. The youngest of the bunch, Jared, entered the NHL in 2008 when he was drafted by the Phoenix Coyotes.