HONG KONG • His long-time girlfriend asked: "May I know what's going on?"

April Leung posted her shock after she was told that Steven Cheung, one-half of Hong Kong musical duo Boyz, had revealed online that he was going to marry a fan called Au Man-man.

Cheung, 34, also posted a picture of him and Au celebrating their son's 100 days.

As other women came forward to say that he had also wooed them, fans lambasted the singer for his straying ways.

On Monday, Cheung finally took to Instagram to address the issue.

Apologising for his behaviour, he acknowledged that he "will not be forgiven".

"However, I still want to tell each and every one of you: I have made a horrible mistake, and I am sorry to you all."

Asking for understanding, he said he wants to change for the better, dropping the "irresponsible" attitude towards relationships that had drawn a backlash.

Cheung thanked Au for standing by him, promising to "take care of her and the baby", even if the path ahead will not be smooth.

Certainly, his career has taken a hit.

Boyz were slated to perform at the Hong Kong Coliseum in September, taking over the slot vacated by Andy Hui after the latter was slammed for kissing TVB actress Jacqueline Wong in a taxi in April.

In his Instagram post, Cheung also said sorry to Kenny Kwan, the other half of Boyz.

Kwan told media that he could not contact Cheung when news of his womanising broke.

In a video that he posted, Kwan, who was in Thailand to work on marketing materials for the Coliseum gig, said: "Why am I by myself right now?"

His voice choked when he spoke about the concert, saying how he had considered it a miracle after years of trying to make it big in the industry.

Now, his dreams are shattered but he is not abandoning Cheung, adding that he believes Cheung will honour his responsibilities.