COPENHAGEN.- Danish architect, Joern Utzon, who conceived the Sydney Opera House, has died aged 90, the director of the Utzon art and architecture centre in Denmark said Saturday to AFP.

"He died overnight at a care centre north of Copenhagen after suffering a heart attack," Adrian Carter told AFP, adding that Utzon had undergone "major surgery" earlier this year which left him in a weakened state.

Utzon was born in Copenhagen as the son of a naval engineer, and grew up in Denmark. From 1937 he studied architecture at the Royal Danish Academy of Fine Arts and worked for Alvar Aalto and Frank Lloyd Wright. He started his own office in 1950 in Copenhagen. In 1957 he unexpectedly won the competition to design the Sydney Opera House, despite the fact that it was his first non-domestic design and his entry did not meet the contest criteria; the designs he submitted were little more than preliminary drawings. One of the judges, Eero Saarinen, described it as "genius" and declared he could not endorse any other choice. In contrast, Ludwig Mies van der Rohe turned his back when introduced to Utzon.

Over several years Utzon gradually made major changes from his original concept designs and gradually developed a way to construct the large shells that cover the two halls, replacing the original elliptical shells with a design based on complex sections of a sphere. Utzon says his design was inspired by the simple act of peeling an orange: the 14 shells of the building, if combined, would form a perfect sphere.

Although Utzon had spectacular plans for the interior of these halls, he was unable to realize this part of his design. In mid-1965 the state Liberal government of Robert Askin was elected and Utzon soon found himself in conflict with the new Minister for Public Works, Davis Hughes. Attempting to rein in the escalating cost of the project, Hughes began questioning Utzon's designs, schedules and cost estimates, and he eventually stopped the payments to Utzon, who was forced to resign as chief architect in February 1966. He secretly left the country days later, never to return.

In an article in Harvard Design Magazine in 2005, Professor Bent Flyvbjerg argues that Utzon fell victim to a politically lowballed construction budget, which eventually resulted in a cost overrun of 1,400 per cent. The overrun and the scandal it created kept Utzon from building more masterpieces. This, according to Flyvbjerg, is the real cost of the Sydney Opera House.

The Opera House was finally completed, and opened in 1973 by Elizabeth II, Queen of Australia. The architect was not invited to the ceremony, nor was his name mentioned.

In March 2003, Utzon was awarded an honorary doctorate by the University of Sydney for his work on the Opera House. Utzon's son accepted the award on his behalf as he himself was too ill to travel to Australia. Utzon has also been made a Companion of the Order of Australia (AC) and given the Keys to the City of Sydney. He has also been involved in redesigning the Opera House, and in particular, the Reception Hall, following an agreement made in 2000. Also, in 2003, he received the Pritzker Prize, architecture's highest honor.

In March 2006, Queen Elizabeth II opened the western colonnade addition to the building that was constructed by Utzon in the last years without having been to Australia since 1966. His son, Jan, took his place in the opening ceremony instead, saying his father "is too old by now to take the long flight to Australia. But he lives and breathes the Opera House, and as its creator he just has to close his eyes to see it."

On 28 June 2007, the Sydney Opera House was declared a World Heritage site