"I thought the collaboration would give birth to a punk rock song but I didn't expect that the song would be so romantic and peaceful," commented one fan on Sina Weibo. "I almost cried when I heard the song, which brought back a lot of memories. I miss the days when I listened to their songs as a high school student, now that we're all not so young anymore," added another fan.

"We wrote the song together to convey our feelings for each other," says Zhang, 37, a Beijing native, who launched his solo career in 2009 and has expanded his career into reality TV. "We both started out as punk bands and we shared the stage at many music festivals. However, we were shy about talking to each other, and we just watched each other's rise in the music scene."

"We were friends back then, but we used to tease each other playfully all the time. But this time, I really want to tell them how talented they are and how much I love their music. The song is a tribute and to our friendship over the past 20 years, and a reunion with old friends," Zhang adds.

"We enjoyed teasing and making fun of one another, which is our way of being friendly. But beneath the jokes and laughs, we both miss our young days of making music and sharing our life experiences as friends," Peng adds.

Born in Beijing, Peng is also an artist and film director, and he designed the cover art for the new single, in which two of the most famous characters in his animation series, Mimi and Gaga, can be seen looking at each other as they sit on a couch together.