Royal Family Will Not Retreat in Wake of ISIS Threat Against Prince George

The Royal Family will NOT retreat from public view in the wake of an ISIS call to action against 4-year-old Prince George ... sources directly familiar with the situation tell TMZ.

As we reported 32-year-old Husnain Rashid encouraged ISIS to attack the boy who is third in line for the throne -- attack him at his school.

Our Royal sources tell us, Prince George is scheduled to appear June 9 with his family on the Buckingham Palace balcony for a ceremony in full public view, and the event will absolutely take place.

As for attending school, the Palace is well aware the location of the school is public record and the boy will continue attending.

The family has almost remarkably been seen in public ... check out this pic taken just last Sunday at a public park where Kate Middleton, Prince George and Princess Charlotte attended the Houghton horse trials.