BTS
BTS, composed of Rap Monster, Jungkook, V, Jimin, Jin, Suga and J-Hope, debuted on June 13 BTS/Facebook

Korean idol group BTS are celebrating their fourth anniversary today and fans around the world trended the event on Twitter.

BTS, composed of Rap Monster, Jungkook, V, Jimin, Jin, Suga and J-Hope, debuted on June 13, 2013 with the album "2 Cool 4 Skool" that contained the title track "No More Dream."

Last night, fans celebrated the anniversary by trending the hashtag #4yearswithBTS, which became No. 1 worldwide on Twitter.

Before the anniversary, BTS celebrated their annual "BTS Festa" with different events.

Jungkook and Jimin released their own cover of "We Don't Talk Anymore" while the group released the dance practice videos for "Not Today" and "I Like It Part 2," Rap Monster and V's ballad "4 O'clock" and stage video clip for "Wings."

News and entertainment organizations in world also congratulated the group.

"@BTS_twt congrats on an amazing 4 years! Was a thrill meeting everyone at the #BBMAs! #4yearswithBTS," tweeted US morning TV show "Good Morning America."

Billboard Music Awards posted, "4 years of @BTS_twt Army happiness. #4yearswithBTS."

"#4YearsWithBTS and hopefully many more to come. #iHeartBTS," tweeted IHeartRadio.

In the last four years, BTS have grown to become one of the most popular K-pop groups not only in Korea but also worldwide.

BTS' humble beginnings started when debuted in 2013 from Big Hit Entertainment, a relatively small entertainment agency in Korea.

After one-and-a-half years, they won their first ever TV music award on May 15, 2015 on SBS' "The Show" with the single "I Need U."

Their popularity exploded worldwide that resulted in their albums charting on Billboard.

Their "Wings" album released last October ranked 36th on Billboard 200, the highest rank achieved by a Korean singer. The album also became the bestselling album in Korea in 2016, according to the Gaon chart.

Last week, BTS achieved a milestone when "Not Today" reached 100 million views on YouTube, their sixth music video to do so. The others are "Fire" "Dope," "Boy in Love," "Blood, Sweat & Tears," and "Save Me."

Last month, they won the Top Social Artist award at the Billboard Music Awards, the first K-pop group to have been nominated and won at the annual awards show.

BTS has massive following on social media. Their Twitter account has 6.19 million followers while their Facebook account has 4.54 million.

Tonight (June 13), the group will meet fans at their BTS Festa Home Party event at Woori Financial Art Hall at Olympic Park in Seoul.