A professor recently discovered that a medieval castle thought to have been lost for centuries was hiding in plain sight — inside a Victorian-era building on a modern college campus.

The discovery was announced by University College Dublin (UCD), in Dublin, Ireland, on Sept. 18.

The school announced in a release — entitled “‘Lost’ medieval castle found hiding inside UCD building” — that medieval archaeology professor Tadhg O’Keeffe found substantial portions of the medieval Roebuck Castle still survive within the university’s present-day building.

The present-day Roebuck Castle retained the name of its medieval predecessor — but the Victorian-looking building was long believed to contain little, if any, of the original castle.

The original structure had fallen into ruin by the 18th century and was later incorporated into a residence that underwent extensive alterations, including a major Victorian makeover in 1874. UCD purchased the property in 1986.

O’Keeffe told Fox News Digital that, despite those centuries of changes, most of the medieval structure is still there.

Medieval archaeology professor Tadhg O’Keeffe discovered substantial portions of the medieval Roebuck Castle surviving inside a Victorian-era building on the University College Dublin campus in Dublin, Ireland. University College Dublin

“I would say that 70 to 80% of the building is still there, hidden under Victorian plaster,” he said.

He began investigating after studying 18th-century watercolors by artist Gabriel Beranger, which depicted the medieval castle before the property underwent major redevelopment.

Around 70 to 80% of the building was still there, hidden under Victorian plaster. University College Dublin

“I wasn’t terribly optimistic,” O’Keeffe said. “When I got into the building and had a look around, I realized that actually, most of the castle is still there, inside the building.

“It’s not obvious to the naked eye,” he continued. “It’s not obvious to a non-expert. But I specialize in medieval castle architecture, and I saw all the indications when I went in that the castle is still there.”

O’Keeffe pointed to unusually thick walls, along with a stone vault and arched stone roof, as evidence of the building’s medieval history. Fox News Digital

The clues were hiding beneath the building’s more modern appearance.

O’Keeffe pointed to unusually thick walls, along with a stone vault and arched stone roof, as evidence of the building’s medieval past.

“The gate tower is very clear on the inside,” he said.

Though you can’t see the original stonework, the splayed windows are an indication of a medieval date. Tadhg O’Keeffe

“Everything is plastered over so you can’t see the original stonework anymore, but it’s all clearly still there,” he said. “Also, the windows are splayed, and splayed windows are a real indication of a medieval date.”

Roebuck Castle was likely owned by ‘people of some significance.’ It’s reputed that King James II lived there briefly in the late 1600s. Tadhg O’Keeffe

Roebuck Castle was likely built in the early 13th century, after the Norman invasion of Ireland began in the late 12th century.

Roebuck Castle also stands out for another reason: Researchers know who owned it through much of the Middle Ages.

“The gate tower is very clear on the inside,” O’Keeffe said. Tadhg O’Keeffe

The owners were “people of some significance,” O’Keeffe added.

“One of them, in modern terms, would be the equivalent of the chief justice in the Supreme Court, the most senior legal person in Ireland for part of the Middle Ages,” the historian said.

“Another resident at one stage, temporarily, was King James II. It’s reputed that he lived there briefly in the late 1600s.”