Nicholas Tse's sister has a baby girl, but who's the father?

Guess what? Jennifer Tse's now a mum.

The Hong Kong model-actress announced on Instagram that her daughter has turned 100 days old by posting a photo of the baby grasping her finger.

In the post, the 36-year-old wrote, "You are my brightest light."

But like her former sister-in-law Cecilia Cheung, she did not reveal who is the father of her child.

The announcement came as a surprise as Jennifer showed no signs of pregnancy when she appeared at a jewellery event in Hong Kong last May.

She also told the media at the time that she was single.

In what seemed like an attempt to hide her pregnancy from the public eye, Jennifer became less active on social media in recent months, and also missed having reunion dinner with her older brother Nicholas Tse and their parents this Chinese New Year.

When contacted by Hong Kong media, Patrick Tse said he didn't know anything about his daughter's partner but said he's happy about his new grandchild.

While her marital status remains a mystery, Jennifer's most public relationship was with Taiwanese-American actor Andy On. The pair started dating in 2009 and called it quits in 2013.

She then dated TV and film producer, Sean Lee-Davies in 2014 for a year.

In 2016, Jennifer was rumoured to be seeing 'Hawkeye' Jeremy Renner when they attended the premiere of his movie Wind River in Los Angeles.

A year later, she revealed in an interview that she met the 48-year-old actor's parents. Jeremy, however, denied the dating rumours in a later interview.

Will Jennifer ever reveal the identity of her baby's daddy? Only time will tell.