Idol group BTS' dreams came true while filming their reality program for Mnet.

The group was greeted by Grammy award winning rapper Coolio when they entered their hotel in L.A. for the July 24 episode of their show.

Coolio worked with the group during his short time with them, imparting his knowledge about the hip-hop scene and allowing the members of BTS to experience the real U.S. hip-hop culture.

The episode of their reality television program will air on Mnet on Thursday.

The seven-member group recently celebrated their 400^th day since debuting. Members Jimin, Jin and J-Hope tweeted on the group's official Twitter account, thanking their fans (A.R.M.Y) for their ongoing support, according to the publication Allkpop.

"Everyone, [it's our] 4. . .0.0. . .day. I'm doing a three0line poem using the world 'Sa Baek Il' (400 days). Sa Sarangheyo [I Love You] A.R.M.Y Beak Bun (100 times) I may sat it, but it wouldn't be enough," wrote J-Hope.

BTS recently performed for a crowd of 200 lucky fans in West Hollywood who were able to enter the concert for free, according to Billboard.

BTS, along with K-pop sensation Girls' Generation, was amongst the first artists to be announced for the KCON 2014 lineup.

The boys of BTS have been dominating the K-pop industry only a year after debuting in May.

They already made their mark on the Billboard charts with their "Skool Luv Affair" album, which ranked No 3 on World Albums chart while their 2014 singles "Boy In Luv" and "Just One Day" each ranked at No. 5 and No. 25 on World Digital Songs, according to the music magazine.

"Boy In Luv" was a milestone for their career as it was the first K-pop Hot 100 track they had this year, ranking at No. 54.

The members of BTS are currently in L.A. working on their upcoming album, according to Hellkpop.