The Duke of Edinburgh will take the lead for the Royal Household in the Windsor Castle rebuilding programme rather than the Prince of Wales, whose hostility to modern architecture is well known.
Prince Philip has already taken part in discussions on the castle, which culminated last week in a meeting between the Department of National Heritage and leading figures from the world of architecture and conservation.
The meeting, at Windsor, included representatives of the Royal Institute of British Architects, which wanted an architectural competition for the rebuilding of St George's Hall; Lord St John of Fawsley, chairman of the Royal Fine Art Commission; Jocelyn Stevens, chairman of English Heritage; and its chief executive, Jenny Page.
Prince Charles has been kept out of discussions to avoid the type of confrontation with architects that became increasingly common in the 1980s.
Michael Manser, a former president of the RIBA, described the Duke's involvement as 'marvellous' news.
'Prince Philip is one of the unsung heroes of British architecture,' he said.
'He has a solid background knowledge about design and designers. Unlike his son, who is deeply emotional and prejudiced when it comes to architecture, Prince Philip has an open mind.'
The roofline of the castle will be restored exactly as it was before. However, the Department of Heritage, supported by English Heritage, says that it would be pointless to try to restore the chapel, where the damage is more radical.
Giving the commission to a leading architect will upset traditionalists, who wanted all parts of the castle damaged by the fire on 20 November last year to be restored as they were or redesigned in line with an earlier era of the castle's history.
The decision to restore St George's Hall, which was remodelled in the 19th century by Sir Jeffry Wyatville, goes against the wishes of the modernist camp, which has argued that it should be rebuilt using materials such as steel and glass.
But it is understood that the Royal Household wanted the hall restored to its original form using traditional materials.
English Heritage says that much of the original Wyatville interior remains intact and this makes it worth restoring. English Heritage experts said: 'Although quite a bit of the ceiling was destroyed, enough of the hall has survived, so it seems sensible to keep it as one piece.'