Legendary crooner Neil Diamond gave his fans a special treat when he sang "Sweet Caroline" impromptu during the opening night of Broadway's "A Beautiful Noise, The Neil Diamond Musical" on Sunday night.

The audience enthusiastically sang along with the 81-year-old singer, who belted the tune from a box seat at the Broadhurst theater in New York.

Theatergoers erupted in applause and gave a standing ovation to the legendary musician, who was performing for the first time in his hometown since 2017.

It was also a rare appearance for the singer as he had announced in 2018 that he was diagnosed with Parkinson's disease and would be retiring from doing concert tours.

"The audience's reaction when they realize it's him is priceless," an Instagram user commented on the musical's official Instagram page.

"I love my Neil. Always has a special place in my heart," another wrote.

A third wrote, "Omg!! I got chills. I love him and this song so much. Neil Diamond is a true living Legend."

Another excited fan also wrote, "I would have passed out."

"Amazing!!! Im shook! We love Neil!" a fan who goes by the handle @Phillyhugs said.

Prior to his surprise performance, Diamond walked the red carpet with his wife, Katie McNeil. The audience rose when he entered the theater. Celebrities who attended the opening night include Audra McDonald, Bernadette Peters, Clive Davis and Jane Krakowski, among others.

Before this, the iconic singer-songwriter also performed the 1969 hit at a Boston Red Sox game in June.

In 2018, Diamond announced on his website that he will no longer be touring due to Parkinson's disease – a brain disorder that causes uncontrollable movements, including difficulty with balance and coordination. Other symptoms include tremor in hands, arms, legs, jaw or head and slowness of movement.

In announcing his retirement, Diamond vowed to "remain active in writing, recording and other projects for a long time to come."

In his long musical career, which began in the '60s, Diamond had sold over 130 million albums, and is known for many other hits including "I'm a Believer," "Red Red Wine," and "Cracklin' Rosie." He was inducted in the Rock 'n Roll Hall of Fame in 1984 and was honored with a Grammy Lifetime Achievement Award in 2018.

Neil Diamond, shown here performing in New York in 2016, has sold his entire catalog to Universal
Neil Diamond, shown here performing in New York in 2016, has sold his entire catalog to Universal GETTY IMAGES NORTH AMERICA via AFP / Theo Wargo