Author and broadcaster Muriel Gray was outside the building as fire tore through its fabric.
The famous graduate, who worked as a professional illustrator and then as assistant head of design in the National Museum of Antiquities in Edinburgh, found fame on the Channel 4 alternative pop show The Tube.
She went on to present Frocks on the Box and The Media Show.
She said: "The important thing is that everyone got out.
"We have that confirmed. It is just devastating."
Her famous fellow former students include photo-graphers, actors and politicians.
Harry Benson, who was born in Glasgow, is a photo-grapher whose pictures have appeared in publications including Life, Vanity Fair, People and The New Yorker.
He was chosen to travel with The Beatles on their inaugural American tour in 1964.
One of his most recog-nizable images shows the band in a gleeful pillow fight in a hotel room.
Playwright and artist John Byrne is best known for The Slab Boys and Tutti Frutti.
Actor Peter Capaldi, who will play the next Doctor Who is also famous for his role as Malcolm Tucker in the BBC comedy series The Thick of It and its spin-off film In the Loop.
Robbie Coltrane found a new generation of fans as Hagrid in Harry Potter, while novelist and muralist Alasdair Gray is the author of Lanark: A Life in Four Books.
Bob Hardy won an army of fans as bassist with Franz Ferdinand and artist Peter Howson also studied at the school, as did Cathy Jamieson, Labour MP for Kilmarnock and Loudoun.
Playwright and poet Liz Lochhead is a former student, along with folk singer and broadcaster Jimmie Macgregor.
Hollywood star Brad Pitt was given a tour of the Mack-intosh Building when he was in the UK filming Interview with a Vampire during the early 1990s.
The actor went on to design a range of furniture which was inspired by the Mackintosh's work.