The actress, currently starring as a mum in ITV drama 'The Guilty', has announced on Twitter that she and her new husband Ryan Clark are to become parents.
She writes: "Ryan & I are overjoyed to announce that we are expecting a baby! Feeling very blessed!"
The baby news comes less than a month after Katherine and Australian Ryan, both 33, jetted to Las Vegas to tie the knot.
Friends have been congratulating 'Mr Selfridge' actress Katherine following the announcement, including 'EastEnders' Jo Joyner.
She tweeted: "Congratulations! Didn't take long! It's going to be fantastic, enjoy every second xx."
Katherine and Ryan have been together for around three years. The couple married at the Little Church Of The West in Sin City in August.
The star told Hello! magazine after her nuptials: "I love going to other people's weddings but I have never desired a big white wedding for myself and it has never been put on me as a pressure, an expectation."
Read the full story in Hello! magazine, out now.