They decided to part ways after their lucrative Behind the Magic tour ended in June as reported by The Sun.
Bychkova, previously engaged to Slovenian footballer Matija Skarabot, attended Wimbledon solo last week, while Widdrington visited friends and family in the US.
The Ukrainian dancer, 34, was supposed to join the 28-year-old at the Police Bravery Awards on July 11, but he ended up attending alone.
The pair wrapped up their tour in June
An insider told The Sun: “It’s heartbreaking. Kai and Nadiya seemed like the most perfect couple and have been so, so blissfully in love.
“But the pressures of touring – being in each other’s space 24/7, and the stress of performing a sell-out show eventually took its toll.
“After a tough few weeks, they sat down together and decided to call it quits. They remain incredibly close and are determined their split will not have any impact on the next series of Strictly – they remain consummate professionals, and nothing will change that.”
The Standard has contacted Nadiya Bychkova and Kai Widdrington’s rep for comment.
News of their split comes as Richard Madeley commented on the ongoing Strictly Come Dancing scandal, as the BBC show faces increasing scrutiny.
While hosting Good Morning Britain with Charlotte Hawkins on Thursday, the 68-year-old expressed his lack of surprise regarding the allegations.
Madeley claimed that he knows many people who have participated in the popular dance show, and these issues have been a topic of conversation for years.
Richard Madeley weighed in on the ongoing Strictly scandal
Previewing the day’s programme, Madeley announced they would be interviewing Strictly alumni Reverend Richard Coles and Edwina Currie about their experiences on the show.
He then added: “I have to say the people that I know involved in that programme all talk about these issues and they say they’ve all known for years and years and years but the lid has been kept on it and now that lid is coming off.”
Madeley’s words came after it was revealed a third Strictly Come Dancing professional has reportedly been named as a ‘person of interest’ in the wake of abuse and bullying allegations overshadowing the show.
A member of the production team will now be present “at all times” during training room rehearsals and there will be a celebrity welfare producer and a professional dancer welfare producer.
Love Island star Zara McDermott, 27, has opened up about her time on the BBC series following the exit of her former professional partner Graziano Di Prima, 30.
Reverend Coles, who appeared on the show in 2017 when he was partnered with Dianne Buswell, said few people involved in the show have been surprised by the allegations.
He told Times Radio: “I remember somebody who worked on the show for years and years telling me: ‘Strictly is a wonderful show with a dark heart.’ And I never really understood what that meant, but perhaps one of the things that meant is what you don’t see, which is how intensely competitive it is.
“And also, I think the fact that it’s so important to the BBC, how much effort goes into maintaining the glitter on the glitter ball.”