Marky Mark is back?! Mark Wahlberg surprises crowd at New Kids on the Block concert!

Marky Mark Joins NKOTB on Stage

It was double the Wahlbergs at New York City's Madison Square Garden on Monday night!

Mark Wahlberg -- formerly known as Marky Mark -- surprised thousands of fans at the New Kids on the Block show when he showed up during his brother Donnie Wahlberg's performance of "Good Vibrations."

This was the first time the Ted 2 star has joined his brother's boy band on stage in over 20 years.

See the Wahlberg brothers through the years:

Mark Wahlberg, Donnie Wahlberg through the years
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Marky Mark is back?! Mark Wahlberg surprises crowd at New Kids on the Block concert!
Donnie Wahlberg and Mark Wahlberg during 1991 MTV Rock 'n Jock Basketball in Los Angeles, California, United States. (Photo by Jeff Kravitz/FilmMagic, Inc)
Mark Wahlberg and Donnie Wahlberg at the premiere of 'The Truth About Charlie' at the Samuel Goldwyn Theatre in Beverly Hills, Ca. Wednesday, Oct. 16, 2002. Photo by Kevin Winter/Getty Images
Mark Walhlberg & Donnie Wahlberg (Photo by SGranitz/WireImage)
Donnie Wahlberg and Mark Wahlberg and guest during 'Boogie Nights' Los Angeles Premiere at Mann Chinese Theatre in Hollywood, California, United States. (Photo by Barry King/WireImage)
Mark Wahlberg, James Wahlberg and Donnie Wahlberg (Photo by J. Vespa/WireImage for Bragman Nyman Cafarelli)
Singer Mark Wahlberg and singer Donnie Wahlberg of New Kids on the Block visit 'The Joan Rivers Show' on December 2, 1992 at CBS Broadcast Center in New York City.
VARIOUS, VARIOUS - JUNE 09: Mark Wahlberg and Donnie Wahlberg of New Kids On The Block pose backstage during a circa 1991 concert. (Photo by Kevin Mazur/WireImage)
Actor Donnie Wahlberg and actor Mark Wahlberg attend the 'Boogie Nights' Hollywood Premiere on October 15, 1997 at Mann's Chinese Theatre in Hollywood, California. (Photo by Ron Galella, Ltd./WireImage)
BOSTON, MA - OCTOBER 24: (L-R) Donnie Wahlberg, their mother Alma Elaine Wahlberg, chef Paul Wahlberg and Mark Wahlberg attend the grand opening of Wahlburgers on October 24, 2011 at the Hingham Shipyard in Boston, Massachusetts. (Photo by Marc Andrew Deley/FilmMagic)

WATCH: New Kids on the Block -- Then and Now

And he wasn't the only surprise star of the night! Rapper 50 Cent introduced Mark to the excited audience, exclaiming that it looked like there were some "good vibrations here tonight."

The 39-year-old hip-hop star was also joined by Biz Markie. The rappers performed their hits "Just a Friend" and "In Da Club."

PHOTOS: New Kids on the Block Flaunt Their Abs on Instagram

NKOTB's Main Event tour has been thrilling fans across the country since they first kicked off their 40-concert series in Las Vegas on May 1. They were also joined by '90s chart-toppers TLC and rapper Nelly.

ET was there during their tour rehearsals. Check it out:

Backstage With New Kids on the Block Before the Launch of World Tour
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