Desmond Sylva, 40, is accused of stabbing nurse Simonne Kerr, 31, in Battersea, south west London, on Wednesday, Scotland Yard said.
Sylva was charged the day after Ms Kerr was found with a knife wound at her home.
The mother-of-two performed as part of the NHS’s B Positive choir, who promote blood donations, on the TV talent show.
Her social media shows a woman who campaigned and donated blood in aid of sickle cell anaemia.
Ms Kerr’s son Kavele died in 2015 from sepsis, a complication arising from his sickle cell disease diagnosis.
Ms Kerr was pronounced dead at the scene in Grayshott Road after police were called to a flat shortly before 12.40pm on Wednesday.
She died around an hour after officers were called despite the efforts of paramedics.
Sylva, of Grayshott Road, will appear at Wimbledon Magistrates Court on 17 August.
Scotland Yard said detectives are not looking for any other suspects.
The haematology and oncology nurse worked at Guys and St Thomas’ Hospital in south London.
Ms Kerr, who is originally from Wembley, spoke about how the NHS choir performances gave her strength after losing her son Kavele to complications from the blood disorder.
“When I’m with the choir, I look either side of me and see new friends who have been affected by the same disease which took Kavele,” she said, reports the Daily Mirror.
“They know the physical and emotional pain of it. We support each other and there’s a real family vibe. When we sing, we don’t just rattle through a song. We sing with real feeling that comes from the bottom of our souls.”
The talent show judges praised the group’s successful performance in this year’s series, with Simon Cowell calling it “amazing”, David Walliams saying it was “inspiring”, and Alesha Dixon declaring it “one of the most soulful, honest, authentic performances that we’ve had on the show”.
Ms Kerr, who carried the disease but was not affected, qualified as a nurse in January and joined the hospital the following month.
Vickie Foot, a 43-year-old who lives nearby, described the killing as “absolutely shocking” and said she saw the arrest.
Ms Kerr’s next-of-kin have been informed and a post-mortem was due to take place on Thursday.