Justin Bieber visits hometown exhibit on himself in Stratford, Ont.

John Kastner said he got a text from Bieber’s grandparents about half an hour before they arrived around noon Friday  (Photo: Justin Bieber/Facebook)

STRATFORD, Ont. — Justin Bieber’s grandparents are known to frequent an exhibit on him in his hometown of Stratford, Ont.

But on Friday the venue got an unexpected visit not just from them — but also from the pop superstar himself.

John Kastner, general manager of the Stratford Perth Museum, said he got a text from Bieber’s grandparents about half an hour before they arrived around noon on Friday.

“It said, ‘We’re just having breakfast. Can we drop by?’ And I said, ‘Sure,”’ he recalled in a phone interview.

“Reception called and said, ‘Justin’s grandparents are here and they have somebody with them’ — and I went downstairs and there was Justin Bieber.”

Sporting a plaid hoodie, khaki pants, shaggy bleached hair and a bit of beard scruff, Bieber spent about 45 minutes in the exhibit.

He arrived sans entourage and about an hour after a bus trip of about 200 students had left the exhibit. During his visit, there were only two patrons.

“He couldn’t have been nicer,” said Kastner. “He couldn’t have been more humble, he couldn’t have been more appreciative.

“He kept saying how fantastic it was, how much he appreciated us doing it, what a great job we did.”

The Steps to Stardom collection opened Feb. 18 and profiles his rise to fame. It has artifacts including Bieber’s Grammy Awards as well as mementoes from his childhood in the southwestern Ontario city.

Bieber took photos with staff and signed a T-shirt that they plan to frame, said Kastner.

The “Sorry” singer was particularly excited by seeing the drum set he used to play as a child busker in Stratford. He was nine when he received it as a gift from three local residents, who held a fundraiser to buy it for him.

He was also thrilled by an old hockey bag of his.

“We have a big blackboard where people can put messages on there to him and he signed right across the top and said, ‘Justin was here,’ and then put a big heart,” said Kastner.

“We’re going to urethane that over so that stays on the board for all eternity.”

Kastner said Bieber’s grandparents, Bruce and Diane Dale, were at the museum nearly every day for the two weeks prior to the exhibit launch.

They continue to visit it, about once a week, but this was Bieber’s first time taking it in.

“He talked about what a great exhibit it was, how it spanned his life, how it was emotional for him,” said Kastner.

“He said a couple of times, ‘Looking at this stuff gives me goosebumps. I never thought there would be a museum exhibit about me.”

The exhibit runs until the end of the year.

It’s been a boon for the museum, which also plans to open an exhibit on late author Harper Lee’s Pulitzer Prize-winning novel “To Kill a Mockingbird” next month.

“This museum, in 2013, did 853 people in the year,” said Kastner, “And on Family Day weekend, we did 1,000 people.”