Paul VI Catholic High School, located in Fairfax since 1983, is pursuing a move to Loudoun County, the Catholic Diocese of Arlington announced Thursday.

The diocese, which oversees Paul VI, said the school is planning to relocate by 2020 to a South Riding property already owned by the church.

“As mayor I’m clearly disappointed in the decision,” said Fairfax Mayor R. Scott Silverthorne. “We worked hard to convince them to stay.”

Sister Bernadette McManigal, the diocese’s superintendent of schools, said in a statement that the relocation would include construction of a new, state-of-the-art campus that would be larger than the school’s current 18-acre facilities along Fairfax Boulevard near Route 123.

The new campus for Paul VI “would further strengthen its heritage as a leading Catholic high school,” McManigal said.

Loudoun County Supervisor Matthew F. Letourneau (R-Dulles), a Catholic high school graduate, lauded the news in a statement.

“Paul VI would provide Loudoun residents with a high-quality educational opportunity and would be a valuable addition to our community,” Letourneau said. “The construction of Paul VI could also bring some relief to Loudoun’s high schools, which face continued strains due to a growing student population.”

The new campus would be built on land located near the intersection of Riding Center Drive and Braddock Road, Letourneau said in a statement. The move comes as Paul VI has experienced significant growth. About 1,000 to 1,200 students attend Paul VI, said Silverthorne, and the school expects to continue expanding.

“The fact of the matter is this decision was largely made because of the size of the campus,” Silverthorne said.

In a statement, the diocese said that incoming freshman for next fall would be guaranteed four years of matriculation at the current campus. Silverthorne said the moving process should take about five to seven years.

Silverthorne said the diocese is intending to sell the property, situated on prime real estate in Fairfax. He cautioned, however, that the current zoning for the property is split between commercial and residential, possibly limiting certain types of development.

“I want us to explore every possibility available for the future use of this site with community input,” Silverthorne said. “For us, this is an opportunity I think to find a win-win that meets the community’s desires.”