Ever since the 1990s, a party is not a party without this song: "Everybody (Backstreet's Back)" is a pop music classic, and most people between the ages of 20 and 60 will sing along.

Released in June 1997, the song had multi-platinum status in numerous countries at the time and sold over 3.6 million copies. It is one of the Backstreet Boys' most successful songs — and yet it was never a number one hit.

Songs for the heart

If the 1990s marked the golden decade of boy bands, the concept of forming a vocal group of young male singers was not new. In the 1960s, a fictional band of four young boys was created a TV sitcom called "The Monkees," and ended up becoming one of the most successful groups of the decade. In the 1970s, the boy band Bay City Rollers broke girls' hearts worldwide, and in the 1980s it was the New Kids On The Block.

By the 90s, competition came from techno music, dramatic grunge rock with its doomsday mood — but young female music fans in particular still wanted feel-good tunes.

The British band Take That filled that void, and they were enormously successful. The voices of the five boy band members including Robbie Williams came together beautifully, and they were great dancers. Their albums sold like hot cakes; their fan base was huge, young and female.

Producers quickly realized that the market for boy bands was huge: East 17, Caught In The Act, *NSYNC followed, along with the Backstreet Boys, founded on April 20, 1993.

Two years of bootcamp

Earlier that year, Nick Carter, AJ McLean, Brian Littrell, Howie Dorough and Kevin Richardson were chosen in a mega boy band audition — 500 young men showed up — in Orlando, Florida.

Music manager Lou Pearlman's new line-up included different roles, aiming to appeal to girls' different tastes — the "nice boy next door," the "rebel," the "dreamy type," the "more mature boy" or the "cute youngster."

For two years, the boys practiced hard, with singing, dancing and choreography lessons. The band was designed as a group of white middle-class boys singing Black music like soul, R'n'B and hip hop — all tailored to the US market.

In October 1995, they released their first single, "We've Got It Going On." The Backstreet Boys were successful in the US, and made a big impact in Europe, too.

They were awarded their first golden record in Germany, and after that, nothing was the same. The Backstreet Boys become superstars overnight, teenagers screamed themselves hoarse and fainted wherever they showed up. Their screaming drowned out the music. What caused The Beatles to stop performing in public 30 years before simply motivated the Backstreet Boys.

Destructive success

The debut album, "Backstreet Boys" (1996), went platinum several times over, followed by sold-out concerts. The second album, "Backstreet's Back" (1997), boasted astronomical sales figures. The band was showered with music awards, and again went on sold-out tours through Europe. In the US, too, their music hit top chart positions.

Success took its toll on the young musicians. Constant availability to fans and the press, pressure to play the roles assigned to them and to break the hearts of female teenagers as well-behaved white heterosexual men — that didn't work out for long.

The band members started to break free of the mold. Nick Carter and AJ McLean were drinking excessively and did drugs. "I could've ended up a tragedy," Nick wrote in his memoir "Facing the Music and Living to Talk About It." "During the height of my problems, I did ecstasy, cocaine and drank a large bottle of vodka a night."

Fans are forgiving...

The tabloid media closely tracked Nick Carter's toxic relationship and eventual break-up with Paris Hilton. But it seems the band's fans are very forgiving, not even turning their backs when Brian Littrell outed himself years later as an ardent Trump supporter.

Breakup rumors, hiatuses and comebacks have not diminished the Backstreet Boys' ongoing success. When Kevin Richardson quit for six years in 2006, the band continued as a foursome.

Their manager Lou Pearlman, who also launched *NSYNC, wound up in prison in 2008 for fraud and money laundering. He died in prison of a heart attack in 2016.

But no matter what happens — every new Backstreet Boys album sells well, to this day.

Nick Carter, now married and a father, faces sexual assault lawsuits. He denies the charges. The vast majority of fans believe their idol is innocent, so the band continue to play to a screaming audience that has remained loyal to them since the 90s.

The DNA World Tour is underway and will soon take the band to Iceland, the Arab countries, the Middle East, India and South Africa. The set list includes songs from their latest album, "DNA" (2019), a cross-section of 30 years of band history and, of course, the band's megahits including "Quit Playin' Games," "I Want It That Way" and "Everybody."

Their fans have aged with them. Even at 40, women can still shriek —though not as shrilly — as well as throw underwear and teddy bears. These days, however, Nick Carter (43), Kevin Richardson (53) and the other Boys fight back: They run backstage, arm themselves with hand-signed panties and throw them at their audience.