Talk about rivalries. Real Housewives of Orange County’s Shannon Beador got into a heated confrontation with her husband David’s former mistress, Nicole McMackin, at a USC football game in Los Angeles on Saturday, Oct. 24, Us Weekly has exclusively learned.

An eyewitness at the event tells Us that the reality star initially tried to ignore McMackin when she first noticed her. (David’s ex-mistress was purposely trying to catch Shannon and David’s attention by walking right by them, the eyewitness says.)

The showdown became unavoidable, however, when Shannon, 51, returned to her seat at one point during the game and ran into McMackin — literally — as she was leaving the tunnel.

“That’s when Shannon calmly said to Nicole, ‘You have a lot of nerve being here,’” the insider says, claiming that Nicole responded by putting her face “two inches from Shannon’s face” and screaming, “F—k you!”

“Shannon followed with an, ‘Are you kidding me?’ to which Nicole replied, ‘You’re sick and you’re crazy,’” the eyewitness continues, saying that Shannon responded with, “Why are you describing yourself to me?”

Shannon then yelled up to the entire section where McMackin was seated, “NICOLE is the woman who had an affair with my husband!” the eyewitness recalls. McMackin seemed unfazed.

Earlier this month, Shannon and David sat down with Bravo host Andy Cohen on Watch What Happens Live to talk about the affair that almost tore their marriage apart, and how they were moving on together as a couple to keep their family together.

“I don’t think that people understand the level of hurt,” Shannon said on the show. “I’m just gonna give an example, okay? When David left me for those two weeks, he would still come and pick the kids up from school. And one day he handed [our daughter] Stella his wedding ring. He said, ‘Give this to your mother, I don’t want it anymore.’”

The couple are also parents to daughters Adeline and Sophie.

Despite the devastation of that statement and David’s eight month-long affair with McMackin, however, the reality pair are determined to get their life back on track.

“We want to give other couples hope even if there is infidelity, or something devastating in a relationship, if you both work and make the effort and love each other, you can get out,” she told Us Weekly back in June. “You can get through it and get through in a better position than you started out in.”