When fans first saw Mandopop king Jay Chou and home-grown singer JJ Lin going around Singapore together in 2018, it was unclear what they were doing.

With the release of Chou's travelogue series J Style Trip on Netflix on March 18, the secret is out.

Lin, 39, is a guest on Chou's show, touring Singapore with him. In return, Chou, 41, surprises Lin's mother at Bishan's Voice Art karaoke lounge, which is opened by Lin's parents.

In the second episode, Lin visits his mother's karaoke lounge and sings for her guests, relatives and friends there. Midway through a rendition of Love Confession, Chou's 2016 hit song, Chou appears suddenly and joins Lin in the singing.

Lin's mother looks surprised and the two stars invite her on stage to sing with them. Chou later performs a magic trick, making roses bloom from a potted plant nearby and giving her one of the roses.

He praises Lin for being a filial son and jokes with Lin's mother: "Did he bring home a daughter-in-law for you? A girlfriend?"

Chou is married to model-actress Hannah Quinlivan and the couple have a daughter and a son. Lin is still single.

In response, Lin's mother asks Chou to introduce women to her son.

In an interview with the travelogue crew, she says: "I always tell my son to be good and to learn from friends around him. Jay Chou is one of them."