Taylor Swift-Themed Party Ends with Two Kids Dead in Mass UK Stabbing

1:47 PM PT -- Prince William and Kate Middleton just weighed in on the tragedy -- writing in part, "As parents, we cannot begin to imagine what the families, friends and loved ones of those killed and injured in Southport today are going through."

They went on to extend their condolences, while thanking first-responders who arrived on the scene.

12:28 PM PT -- Officials have now confirmed even more tragic news from this horrific incident -- namely, the fact that a second child has now died.

In addition to this ... cops have identified the alleged perpetrator as a 17-year-old male. His name has yet to be released -- and it's unclear if the authorities plan to do that.

A Taylor Swift-themed dance workshop in the UK turned into something straight out of a horror movie ... when a mass stabbing left a young girl dead and 7 others injured.

The terror struck Monday in Southport, England ... when an unidentified knife-wielding maniac decked out in a black hood went on a rampage at a kids' dance and yoga workshop attended by at least 25 young girls -- aged 6 to 11.

All of the injured victims were rushed to 3 local children's hospitals ... but tragically, one young girl didn’t make it.

Police were able to track the suspect and take him into custody

Reaction to the violence opened a window into how the world views the U.S. -- one local resident told the BBC, the chaos and violence felt like something you’d see in America, not Southport ... which is usually known for its calm and pleasant vibe.

UK Prime Minister Keir Starmer also condemned the horrendous news on X ... sharing his thoughts with those affected and thanking the police and emergency services for their quick response.

Merseyside Police have the suspect in jail, but so far, they haven't revealed a motive behind his actions.