The Queen's decision not to attend the civil marriage ceremony of Prince Charles and Camilla Parker Bowles is not a snub, Buckingham Palace insists.
The wedding is due to take place on 8 April in Windsor Guildhall
The Queen will attend the church blessing afterwards and is happy to host the reception, the palace said.
But she will not be a guest at the civil ceremony at the Guildhall in Windsor on 8 April.
A palace spokeswoman said the decision had been made because the royal couple "wanted to keep the occasion low key".
"The Queen and the rest of the Royal Family will, of course, be going to the service of dedication at St George's Chapel, Windsor Castle," the spokeswoman said.
"She is very pleased to be giving the wedding reception at the Castle."
Prince William and Prince Harry, along with Mrs Parker Bowles' children, Tom and Laura, are planning to attend the civil ceremony.
The spokeswoman said: "The Queen's prime concern is that the civil ceremony should be as low key as possible, in line with the couple's wishes."
Asked if this was a royal snub, the spokeswoman replied: "The Queen is attending the service of dedication and paying for the reception - this is not a snub."
Historian Dr David Starkey said "one can only speculate on the reason" behind the Queen's decision.
"It could be security, that she doesn't approve, or that she doesn't care - a position which would unite her with the majority of her subjects," he added.
Lord St John of Fawsley, a constitutional expert who knows Prince Charles, said the Queen had made a "good decision" not to attend the civil ceremony and it was a decision she had made amicably with the engaged couple.
"It's not a snub, that really is quite dotty," he told BBC News.
He said she had clearly shown her approval of the wedding but as Supreme Governor of the Church of England "does not want to go to a wedding at a register office".
The Queen was a principled person, he said, adding: "One cannot live one's life in accordance with the way the media may react."
BBC royal correspondent Nicholas Witchell said the Queen had "concerns and anxieties" about the wedding.
"The Queen, in her heart, doesn't feel entirely at ease with this marriage," he said.
Camilla's engagement ring had belonged to the Queen Mother
The marriage ceremony was to have been held at Windsor Castle but was switched last week amid concerns over the licence.
Apparently, royal aides failed to realise the licence required would have run for three years, meaning anyone could apply to marry there during that time.
The Sun newspaper's royal photographer, Arthur Edwards, branded the arrangements for the wedding so far as "a catalogue of cock-ups".
"This is a lame excuse. The reason she is not going, it seems to me, is that it is a civil ceremony in a register office and she does not feel she should be there."
Royal expert Dickie Arbiter agreed. "I think any parent would be a bit fed up with the way this has unfolded.
"When it was announced there was a tremendous fanfare but the goalposts have moved considerably."
And he warned: "I do not think we have seen the end of it, there will be a lot more to come."