Sarah and Todd Palin Had Dinner with Dean Cain Just Months Before Split: 'They Were Completely Normal'

"What happens behind closed doors, and how people grow and change over time is something no one can ever predict or understand, save those two people," Cain tells PEOPLE

News of Sarah Palin‘s pending divorce from Todd Palin comes as a surprise to many — including friend Dean Cain, who had dinner with them at their Alaska home just a few months ago, he tells PEOPLE.

“They seemed wonderful together,” says the actor, 53. “I’d hate to speculate on the cause — what happens behind closed doors, and how people grow and change over time is something no one can ever predict or understand, save those two people.”

“I know that they’re both extremely devoted and wonderful parents,” he continues, “and I’m certain that they’ll both remain dedicated to Trig and their other children.”

Cain, who appeared with Todd, 55, on NBC’s 2012 competition series Stars Earn Stripes, says he just “dropped by” on the former first couple of Alaska. Sarah, 55, made him and some friends dinner at their lakeside Wasilla property.

“They were so warm and gracious, and completely normal,” Cain says. (That may have surprised his friends, he says, but not him.)

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The Stars Earn Stripes cast in 2012. Trae Patton/NBC/NBCU Photo Bank via Getty

According to court documents and online records reviewed by PEOPLE, Todd filed for divorce on Friday. His complaint, dated Aug. 27, cites “incompatibility of temperament between the parties such that they find it impossible to live together as husband and wife.”

He is seeking joint custody of their 11-year-old son, Trig, according to the complaint, and fair division of their assets.

The divorce proceeding lists the plaintiff and defendant only by their initials — T.M.P. and S.L.P. But Todd’s middle name is Mitchell; Sarah’s is Louise. The listed birthdates for both parties also match the Palins’ birthdates, and the filinglists their same marriage date and the birthdate for Trig.

(A listed attorney for Todd didn’t immediately respond to PEOPLE’s request for comment; neither he nor Sarah immediately returned messages.)

The Palins celebrated daughter Piper’s high school graduation together in May but spent Fourth of July apart.

The two eloped in 1988 and have five kids together.

“Family is everything to them,” Cain tells PEOPLE. “I just hope they remain civil and good friends throughout this ordeal.”