(CNN) Edward Nixon, former President Richard Nixon's youngest and last surviving brother, died Wednesday. He was 88.

He had been living in a skilled nursing facility in Bothell, Washington.

In the past 25 years since Richard Nixon's death, Edward Nixon had become "our family's rock," his nieces, Tricia Nixon Cox and Julie Nixon Eisenhower, said in a statement.

"He was a source of guidance to our father, whose favorite little Eddie grew up into a renowned geologist with an infectious curiosity," they said. "He was always thinking, always working -- never for his own benefit, but to uncover the answers to questions that science poses in our world."

An undated photo of Edward Nixon, who was 17 years younger than his brother Richard.

Edward Nixon shared a special bond with his brother.

"Dick was more than a brother," he wrote in 2009. "At the time of my birth, he was 17 and getting ready to start college. But he realized he could be an important influence in my life, and he took his self-imposed responsibility seriously, always listening to his kid brother."

"Through thought-provoking questions, he encouraged me to learn and solve problems," Edward Nixon wrote. "More than anyone else in my family, he could stand back from a contentious situation and give impartial and convincing advice."

He worked on his brother's presidential campaigns in 1968 and 1972, serving as co-chairman of the Nixon re-election committee.

Traveler, geologist

Born on May 3, 1930, Nixon was the fifth and youngest son in his family, and was named Edward after an English king, as was family tradition.

He served in the United States Navy as a naval aviator, helicopter flight instructor, assistant professor of naval science at the University of Washington and Naval Reserve captain, according to the Richard Nixon Foundation. Nixon received his bachelor's degree from Duke University in geology and later got a master's in geological engineering from North Carolina State University.

Edward Nixon, youngest and last surviving brother of President Richard Nixon, passed away this morning near his home in Washington at 88. Statement from President Nixon's daughters and more about Ed's life here: https://t.co/4NHYu51Qj3 pic.twitter.com/LG4VD90mCn — Nixon Foundation (@nixonfoundation) February 27, 2019

He became an expert on global energy use, and spent 60 years studying the uses of natural resources around the world, and often served as an adviser to companies in the field of Earth science.

According to the Richard Nixon Foundation, Edward Nixon had traveled across the globe six times.

"During his 88 years, he was an ideal mentor and source of strength, whether in the Navy, as a distinguished member of the scientific community, or on his goodwill journeys all across the world," his nieces said.

He leaves behind his two daughters, Amelie Peiffer and Elizabeth Matheny.