Knowles married his first wife in the 1990s. After separating from her, he lived with presenter Suzi Perry until September 2003, after meeting on set whilst shooting "City Hospital" for the BBC in 2000. He dated his second wife Jessica Rose Moor from 2009 and they married in September 2012. The couple have a son, Edwin, born August 2014, but announced they were separating in January 2016. He tweeted support for Jessica in July when she was diagnosed with cervical cancer.