The 34-year-old star, who has known the 32-year-old for seven years, is rumoured to have only struck up a romance with the part-time model last year.
Her spokesman told MailOnline: 'Alesha Dixon and her partner Azuka Ononye are delighted to announce they are expecting their first child later this year.'
Pregnant: Alesha Dixon is expecting her first child with boyfriend Azuka Ononye
A friend told The Daily Record: 'Alesha has always wanted to be a mum and is very excited about it. She is very happy.'
News that the friends had embarked on a romance broke last year when they were spotted holidaying together in Marbella.
Mother-to-be: Alesha has just wrapped the series finale of Britain's Got Talent, and is about to start Your Face Sounds Familiar
They met back in 2006 as Alesha embarked on her solo career following the split of her former band Mis-Teeq.
The Nigerian dancer, known as Az, has been in Alesha's life since the breakdown of her marriage to former So Solid Crew member MC Harvey that same year.
Harvey has since spoken out about his highly-publicised affair with Javine Hylton, which led to the split with Alesha.
The singer and presenter, who has remained tight-lipped about her relationship with Azuka, has recently signed up to host new ITV show Your Face Sounds Familiar.
Starting on June 29, Alesha will present the new talent contest alongside Paddy McGuinness, as various celebrities perform as well-known musicians every week.
Marriage breakdown: Alesha was married to former So Solid Crew member MC Harvey until 2006