On Sept. 11, 2001, Air Force One, carrying President George W. Bush, got warning of a mysterious jet flying too close to it, the pilot says.

Col. Mark Tillman said the Air Force One received a message that said Angel is next, referring to the classified call sign of Air Force One, according to the Daily Mail.

Bush was informed of the attack that destroyed the World Trade Center while visiting a school in Sarasota, Fla.

As we got over Gainesville, Fla., we got the word from Jacksonville Center. They said, 'Air Force One, you have traffic behind you and basically above you that is descending into you, we are not in contact with them - they have shut their responder off', Tillman told the Mail.

The senior pilot said this information was shocking as they did not have a clear picture yet about the capabilities of the terrorists. He said they believed someone was following the presidential jet in Sarasota as they had seen it taking off.

He then flew the Boeing 747 out into the Gulf of Mexico to see if the other plane would follow and asked for fighter support. If an airliner was part of the attack, it would be good to have fighters on the wing to go ahead and take care of us, he said.

Tillman said the plan to fly to Washington D.C. was scrapped eventually and the president landed at air force bases in Louisiana and Nebraska from where he addressed the nation.