According to People magazine and E! News, the 39-year-old “A Teacher” actress took to Instagram to share the news, posting a photo of the couple holding hands.
“There are three of us in this pic,” Mara captioned the post.
Bell, 36, and his ex-wife, actress Evan Rachel Wood, also share an 8-year-old son, Jack, according to People.
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Photos: Kate Mara through the years Here are some memorable photos of actress Kate Mara through the years. (Charles Sykes/Invision/AP)
Photos: Kate Mara through the years 2002: Actress Kate Mara arrives at the premiere of the film "Tadpole" on July 15, 2002, in New York City. (Lawrence Lucier/Getty Images)
Photos: Kate Mara through the years 2005: Actress Kate Mara arrives at the premiere of "Brokeback Mountain" at the Mann National Theater on November 29, 2005, in Westwood, California. (Frazer Harrison/Getty Images)
Photos: Kate Mara through the years 2006: Actors Matthew McConaughey (left) and Kate Mara pose at the afterparty for the premiere of Warner Bros.' "We Are Marshall" at the Chinese Theater on December 14, 2006, in Los Angeles. (Kevin Winter/Getty Images)
Photos: Kate Mara through the years 2007: Actresses Emilie de Ravin (left) and Kate Mara arrive at the Monique Lhuillier Salon opening held at the Monique Lhuillier Boutique on October 10, 2007, in Los Angeles. (Frazer Harrison/Getty Images for Monique Lhuillier)
Photos: Kate Mara through the years 2008: Designer Zac Posen (right) and actress Kate Mara arrives to the Metropolitan Museum of Art Costume Institute Gala, Superheroes: Fashion and Fantasy, held at the Metropolitan Museum of Art on May 5, 2008, in New York City. (Andrew H. Walker/Getty Images)
Photos: Kate Mara through the years 2009: Actress Kate Mara arrives at the Annenberg Foundation's Opening Night Gala held at the Annenberg Foundation's Space for Photography on March 26, 2009, in Los Angeles. (Alberto E. Rodriguez/Getty Images)
Photos: Kate Mara through the years 2010: Actors Rooney Mara (left) and her sister, Kate Mara, pose at the premiere of New Line's "A Nightmare on Elm Street" at the Chinese Theater on April 27, 2010, in Los Angeles. (Kevin Winter/Getty Images)
Photos: Kate Mara through the years 2011: Actress Kate Mara arrives at the 17th annual Screen Actors Guild Awards held at the Shrine Auditorium on January 30, 2011, in Los Angeles. (Jason Merritt/Getty Images)
Photos: Kate Mara through the years 2012: Actresses Olivia Wilde and Kate Mara attend the "DeadFall" Premiere during the 2012 Tribeca Film Festival at the Borough of Manhattan Community College on April 22, 2012, in New York City. (Craig Barritt/Getty Images)
Photos: Kate Mara through the years 2013: Actress Kate Mara arrives at the 65th annual Primetime Emmy Awards held at Nokia Theatre L.A. Live on September 22, 2013, in Los Angeles. (Jason Merritt/Getty Images)
Photos: Kate Mara through the years 2014: Actress Kate Mara attends the "Charles James: Beyond Fashion" Costume Institute Gala at the Metropolitan Museum of Art on May 5, 2014, in New York City. (Larry Busacca/Getty Images)
Photos: Kate Mara through the years 2015: Kate Mara attends the "China: Through the Looking Glass" Costume Institute Benefit Gala at the Metropolitan Museum of Art on May 4, 2015, in New York City. (Dimitrios Kambouris/Getty Images)
Photos: Kate Mara through the years 2016: Jamie Bell (left) and Kate Mara attends the "Manus x Machina: Fashion In an Age of Technology" Costume Institute Gala at Metropolitan Museum of Art on May 2, 2016, in New York City. (Larry Busacca/Getty Images)
Photos: Kate Mara through the years 2017: Kate Mara attends the 2017 AMD British Academy Britannia Awards Presented by American Airlines and Jaguar Land Rover at the Beverly Hilton Hotel on October 27, 2017, in Beverly Hills, California. (Frederick M. Brown/Getty Images)
Photos: Kate Mara through the years 2018: Actors Rooney Mara and Kate Mara arrive at the Animal Equality's Inspiring Global Action Los Angeles Gala at the Beverly Hilton Hotel on October 27, 2018, in Beverly Hills, California. (Gregg DeGuire/Getty Images)
Photos: Kate Mara through the years 2019: Kate Mara attends the 76th annual Golden Globe Awards at the Beverly Hilton Hotel on January 6, 2019, in Beverly Hills, California. (Jon Kopaloff/Getty Images)
Photos: Kate Mara through the years 2021: Kate Mara arrives at Disney's "From Your Car" (FYC) presenting FX and 20th Television's "A Teacher" at the Rose Bowl on June 7, 2021, in Pasadena, California. (Kevin Winter/Getty Images)
Photos: Kate Mara through the years 2022: Kate Mara attends the premiere of "The Big Lie" during the 2022 Tribeca Film Festival at Studio 525 on June 10, 2022, in New York City. (Rob Kim/Getty Images for Tribeca Film Festival)
