Despite constant rumours of a break-up, Chinese singer and former K-pop boyband member Lu Han and his Chinese actress girlfriend Guan Xiaotong are still going strong.

Lu, 30, wished Guan happy birthday on Chinese microblogging site Weibo at exactly midnight on Thursday (Sept 17) when she turned 23.

Lu has done so for the past three years.

In his a post, accompanied by Guan's picture, he said: "Happy birthday, cheerful girl."

She commented: "Thank you, cheerful guy."

The couple reportedly fell in love on the set of romance drama Sweet Combat (2018).

When they announced their relationship in October 2017, the news sent fans into such overdrive that Weibo crashed briefly after traffic soared.

The lovebirds have had to battle break-up rumours for most of their relationship, including one earlier this year which speculated that they had broken up when they did not post anything romantic on social media for Chinese Valentine's Day on Aug 25.

Guan is known for her work on series like To Be A Better Man (2016) and more recently, Twenty Your Life On (2020).

Lu left the South Korean-Chinese boyband Exo in 2014 and has since pursued a solo career in China.