Simon Cowell's mansion was burgled in the early hours of yesterday morning (04.12.15) while he and his family were asleep.
The 56-year-old music mogul, his girlfriend Lauren Silverman, 38, and their 22-month-old son Eric were asleep in the luxurious property in Holland Park, West London when the burglar broke in and stole cash and jewellery.
A source said: "Unfortunately security was anything but safe. The burglar found the key and 'bingo,' he was in.
"Some of the gems were sentimental and there was some cash in the safe.
"The value of what was taken is well into six figures."
Simon's bodyguard was woken by an alarm being activated at 2.20am, but by that time, the burglar had already left the scene of the crime.
Simon and his family are all said to have been shaken by the incident.
An insider told The Sun newspaper: "Obviously Simon and Lauren are really badly shaken by this.
"It is a horrible violation of their privacy. But more than anything they are incredibly relieved no one was hurt.
"As upsetting as it is, Simon can cope with losing possessions, as long as his family are safe. That is his one and only concern.
"Still, it's incredibly worrying and he is obviously going to review security.
"He likes to live as normal a life as possible and doesn't want his house to be like Fort Knox, but his family need to feel safe in their own home."
Forensics officers have since examined the scene of the incident and a police investigation is ongoing.