It was marked “return to sender.”

Melissa Fahy, a sixth-grade science teacher at Roosevelt Intermediate School in Westfield, N.J., and her husband were doing extensive renovations on their home last week when they came upon a 72-year-old letter hidden inside a stairwell.

It was Fahy’s father, in town to help the couple with the work, who discovered the hidden treasure — a letter from a pregnant wife to her husband, Rolf Christoffersen, who was serving in World War II.

When her father first showed her the letter, Fahy said her initial reaction was an urge to find the rightful owners.

“This belonged to someone … this isn’t ours,” she said.

And that’s when she took to the active Westfield, NJ Moms Facebook group for advice.

The group, which boasts more than 4,000 members, quickly went to work. Member Carol Bregman Gross was the first to locate Rolf Christoffersen Jr., an associate professor of biochemistry and molecular biology at UC Santa Barbara and the son of Virginia and Rolf Christoffersen.

“Within 45 minutes after posting a photo of the envelope, I was on the phone with a relative,” Fahy told TAPinto Westfield.

The letter was overnighted to Christoffersen Jr., who read it to his now 96-year-old father.

“My father and mother wrote many letters during the war,” the younger Christoffersen said. “They were all lost when we moved to California in 1959.

“The one that Melissa found is the only remaining one, and that is why it is so important to our family.”

The elder Christoffersen, who lives in suburban Los Angeles, was able to hear the words of his late wife when his son read to him from his mother’s note.

“He was very moved by the letter,” the son said. “He did not remember if he had ever had a chance to read it or not.”

Christoffersen was serving overseas with the allied Norwegian navy during World War II while his wife, Virginia, lived at the two-story house in Westfield with her father. When she wrote the letter, she was expecting a child — Rolf Jr.’s sister.

Before Virginia Christoffersen became a full-time stay-at-home mom, she worked as an advertising copywriter in New York, which is when she likely typed the lunch-break love letter to her husband overseas.

“I just feel happy and proud to be carrying the baby of the person I love most in the world,” she wrote in her letter dated May 4, 1945. “I really feel as if I have a part of you with me all the time.

“Are you as lonesome for me as I am for you?” the letter asks. “Sweetheart I am longing for you to come home to Westfield …”

According to Christoffersen Jr., after the war his father had to work three jobs to support his family.

“Because he served in the Norwegian navy, he was not eligible for the GI Bill or other benefits provided to U.S. veterans,” he explained.

This ultimately inspired a 1959 move to California, where Virginia Christoffersen felt her children could be educated in the low-cost state public colleges and universities.

“None of us wanted to leave our home in Westfield but, in the end, we all went to college and have had successful lives in California,” said Christoffersen Jr., who earned his Ph.D. from UCLA.

“So I guess we learned that moms always know what’s best,” he said.

Virginia Christoffersen died May 13, 2011, at age 92.

— Kate Brochu is a reporter with TAPinto Westfield in Westfield, N.J. This story is republished with permission. Follow TAPinto Westfield on Twitter: @WestfieldTAP and connect with TAPinto Westfield on Facebook.