"He got married before he deployed," Lt. Beth Teach, a Navy spokeswoman, confirms.
Although the couple planned an official wedding in November, and sent invitations to friends and family, Keating – the grandson of notorious financier Charles Keating Jr. – took steps to make sure he was married before going into harm's way, friends tell PEOPLE.
"He wanted to protect her in case anything happened to him," says a fellow SEAL.
"It was a well-guarded secret," says friend Robert Whitley, who met the couple through the San Diego wine community, where Brooke is a well-known wine judge's concierge.
It is not uncommon for couples to get married before the service member deploys, Teach explains.
"There are certain benefits to being married, and a lot of couples put that in place as a protective measure," she says.
"Charlie may have had a feeling about this mission," the SEAL friend says. "Maybe he was just being prudent. This is a terrible loss to Brooke and to all of us."
Says the SEAL friend: "This is a comfort no one wants to rely on. But he did right by Brooke. God bless him."
Courtesy Liz Keating
Whitley also praised his friend for making the brave decision to join the elite Navy unit.
"I so admired Charlie," Whitely says. "He could have easily taken a different path and led a comfortable life doing something else. All of us are grief-stricken."
The 31-year-old's death marks the third American service member to be killed in direct combat since U.S. forces began fighting ISIS.
Army Master Sgt. Joshua Wheeler, a member of Delta Force, was killed during a raid on an ISIS compound last October, and Marine Staff Sgt. Louis Cardin of Temecula, California, was killed in action on March 19.