ISIS threatened four-year old Prince George saying, "Even the royal family will not be left alone".
The extremists allegedly posted a picture of the future king on encrypted instant messaging app Telegram with the message, reports The Sun UK on Sunday.
A picture of the young royal outside his £20,000-a-year school in Battersea, South London, was also reportedly shared on the app along with the school's address and the comment "school starts early".
The message allegedly also included words from a jihadi song which translate as, “When war comes with the melody of bullets, we descend on disbelief, desiring retaliation”.
A Daily Star UK investigation uncovered the messages, and were told by security experts it was critical to monitor the messaging service.
Telegram has been branded a "breeding ground" for terrorists after ISIS extremists behind the 2015 Paris attacks used the encrypted messaging app to spread propaganda.
This isn't the first time ISIS have threatened a member of the royal family.
Just last month, a disturbing extremist video challenged Prince Harry to fight jihadis.
They also targeted the Queen in 2015.