They may have each forged successful acting careers, but sisters Rooney and Kate Mara actually come from an incredible sporting background.

The siblings, who recently collaborated on their first movie together, are heiresses to not one, but two, successful NFL teams — with a whopping $20billion empire. Read on to get to know more about their surprising family background…

Their great-grandfather's each founded NFL teams

Rooney and Kate's great-grandfathers each founded NFL teams, and remarkably, it cost them each just $500 to do so. Their great-grandfather on their paternal side is New York Giants founder Tim Mara, while on their maternal side, their great-grandfather Art Rooney Sr. is Pittsburgh Steelers founder Art Rooney Sr.

Now the teams are worth $8.7 billion and $12 billion respectively.

​Kate and Rooney's parents (pictured) are both still involved in their family teams; Chris Mara is vice president of the Giants and their mom Kathleen's brother Art Rooney II is in charge of the Steelers.

Paying homage to their family background

The Girl with the Dragon Tattoo actress Rooney was actually born Patricia Rooney Mara, but chose to use her middle name as her stage name. It also pays homage to her family lineage, with both of her great-grandparents' surnames together.

You may also like

They have favourite teams

While Kate has previously joked that her favourite of the two teams depends on which of her parents she is mad at, she has since revealed that primarily she is a New York Giants fan, for whom her dad is vice president.

"My dad has worked for the Giants my entire life. I grew up at Giants Stadium and I'm a New Yorker, so I do feel closer to the Giants. That's what I grew up with," she said. "I still love the Steelers, and if they played each other [in a Super Bowl], it would be great."

Kate Mara has sung for both teams

House of Cards star Kate has sang the national anthem at both teams' games, both before and after finding fame. In 2005, she sung at the Met Life Stadium in the week that her grandfather, Wellington Mara, passed away.

Their teams have won 10 Super Bowl rings

Each of the teams have achieved huge success in the Super Bowl, with the Steelers winning six times and the Giants claiming four wins.

According to reports, Kate and Rooney's mom has made a bracelet out of the facing and stones from her Super Bowl rings, which she wears on special occasions.