"They're going their separate ways," an insider told The Sun. "It's very sad but they have grown apart and fallen out of love."
Denise, 39, and Lee, 32, who have a three-year old daughter Betsy together, cited their busy work schedules as a reason for their split, according to the newspaper.
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Just last week the trio were seen enjoying a family day out at the Tickety Toc launch party at London's world-famous toy store Hamleys. Denise, Lee and Betsy were all smiles as they posed for cameras and Betsy showed she was every bit the daddy's girl as she clung onto her father.
Over the past few months, however, the young parents have not had much chance to see each other, with Denise promoting Strictly Come Dancing and hosting her Magic FM radio show in the UK, and Lee busy pursuing stardom in Los Angeles and attending auditions.
After a brief spell in the US, Lee returned to London in May but by then the distance had proved too much and the couple's relationship has been under strain.
Reports that their marriage might be in trouble were reinforced when Denise was photographed holidaying alone without Lee in Dubai. The mother-of-one soon put the rumours to rest, revealing that their decision not to employ a nanny meant that she and Lee were forced to holiday separately.
Denise has previously described their relationship as being "like passing ships in the night" because of their busy careers.
"To be honest, it is really difficult," she told Now magazine. "We just haven't seen each other. I started on Strictly in September and we've been like passing ships in the night. I'm not going to lie, it's been a massive strain on the relationship."
Denise and Lee first met while filming the BBC talent show Any Dream Will Do in 2007 and married in April 2009. Their daughter Betsy was born on 1 May 2010.