The wife of one of the three first responders killed by a Minnesota gunman during a multi-hour armed standoff early Sunday said she knew immediately that her husband was dead when a police cruiser pulled up to the family home later that morning.

Cindy Elmstrand-Castruita said she is heartbroken after Burnsville officer Paul Elmstrand — her high school sweetheart and father of her two children, a 2-year-old and a 5-month-old — was slain along with a fellow officer and a paramedic as they responded to an active shooter who had barricaded himself in his house with his family.

The grieving widow said she initially had no idea what happened to her husband during Sunday’s shooting, and was puzzled over an early morning text she got from a friend saying they were sorry for what she was going through, CBS News reports.

Although she initially chalked it up as a mistake, she said she knew what was coming when a police car pulled up in front of her home.

“I looked out my bedroom window and saw a squad car out there,” she told the outlet. “I knew. That’s when I knew he was gone.”

Elmstrand-Castruita said she was proud of Paul, 27, and knew that he likely did everything he could during Sunday’s incident to protect the kids caught in the standoff.

The shooter, identified by authorities Monday night as Shannon Gooden, 38, had holed himself up along with a woman and seven children between the ages of 2 and 15.

“I think he just had to be the hero. He had to do what he thought was right to protect those little lives even if it meant putting his at risk,” Elmstrand-Castruita said, “and it breaks my heart because now he’s gone. But I know that he thought what he did was right.”

She described her late husband as the “most generous, loving, patient person” she’s ever known, adding that he always took his job seriously and was quick to “drop everything to help someone who was in need.”

Paul joined the Burnsville Police Department in 2017 and tied the knot with Elmstrand-Castruita the following year.

Paul, alongside Officer Matthew Ruge, 27, and firefighter Adam Finseth, 40, were gunned down early Sunday during the dramatic confrontation in Burnsville, about 15 miles south of Minneapolis.

A fourth officer was injured in the shooting, but is being treated for non-life-threatening injuries, police said.

The gunman, whose motive is still under investigation, died at the scene from what appeared to be a self-inflicted gunshot wound. Officials have yet to confirm Gooden’s cause of death.

Gooden wasn’t legally allowed to possess firearms, according to court records. He was also involved in a legal dispute over the custody of his three oldest kids.

Police were responding to a domestic abuse call, and following the exchange of gunfire, the woman and children were safely removed from the home, police said.

Echoing Elmstrand-Castruita’s grief, the Minnesota Police and Peace Officers Association paid respect to Paul and Ruge, who were the first two killed in the armed standoff.

“Our law enforcement community is heartbroken. We’re just devastated at the horrific loss,” the association said in a statement. “These heroes leave behind loved ones and a community who will forever remember their bravery and dedication to keeping Minnesotans safe.”

Paul and Ruge were the fifth and sixth officers in the US killed by gunfire so far this year, according to the Officer Down Memorial Page, which records instances of fallen cops.

With Post wires