A missing part of Stonehenge was returned more than 60 years after a British man removed the piece during restoration work at the site back in 1958, according to English Heritage, which looks after the ancient site.

The thin, drilled-out core of one of the large sarsen stones was believed to have been lost for good until Robert Phillips decided to return it just before his 90th birthday.

In the 1950s, Phillips was an employee of an excavation company doing restorative work at the archeological site. But after the work was completed, he took the piece with him, even taking it to United States when he emigrated in the 1970s.

The ancient monument in southern England was erected more than 5,000 years ago and is believed to have been used to track the cycles of celestial bodies.

"The last thing we ever expected was to get a call from someone in America telling us they had a piece of Stonehenge," English Heritage's Stonehenge curator Heather Sebire said in a press release.

The 108-centimetre-long stone core is one of three pieces that was drilled out so that metal rods could be inserted to help keep the massive stone upright.

"Studying the Stonehenge core's 'DNA' could tell us more about where those enormous sarsen stones originated," Sebire said. The returned “incongruously pristine” stone core will be added to English Heritage's collection of more than 500,000 artifacts.

During excavation digs in 1958, cracks were discovered in one of the giant stones and the diamond-cutting business Van Moppes was hired to reinforce it.

Phillips was part of that company that then drilled out the cores to insert metal rods to keep the large stone standing.

But after helping with the work, he held onto the core and even went on to display it in his office. He took it with him when he moved to New York in 1976.

As he moved across the United States over the decades, he made sure to also take the core with him. But the night before his 90th birthday, he told friends and family it was his wish to return the piece he’d taken.

Phillip’s sons Robin and Lewis recently travelled to Stonehenge themselves to return it on his behalf.

“Our father has always been interested in archeology and he recognized the huge importance of the piece of the monument in his care,” Lewis Phillips said in a statement.

But the two other drilled-out cores of the stone pillar are still missing. “It would be fascinating to know where the other two cores went, or indeed if there any other missing pieces out there that might be returned one day,” Robin Phillips said.

English Heritage said having at least one of the missing pieces has offered a “unique opportunity” to analyze where the stones came from.

For decades, archeologists have debated where the large sarsen stones came from. Researchers are still making ongoing discoveries from the site. Some new findings were made as recently as February.

Ongoing maintenance work has been taking place at Stonehenge since the former landowner Cecil Chubb handed over the property rights to the British government in Oct. 26, 1918.