AILEEN Stewart was puzzled when a royal invitation landed in her

letterbox late last week. Why on earth did the Prince of Wales want her

to go to Holyroodhouse in Edinburgh tomorrow to view his latest

collection of watercolour paintings?

After all, the 26-year-old photographer from Stirling is the first to

admit that she is not an expert art critic. Furthermore, while she has

on several occasions managed to capture the Prince on film during

previous royal visits, barely a word has ever been spoken.

''It was certainly a bit of a mystery when the invitation came in,''

she said yesterday, ''and I must admit that the thought crossed my mind

several times that it may be a little joke by some of my friends.

''However, I have checked it all out and the invitation is, in fact,

genuine.''

It would appear that the organisers of the Youth Business Trust, set

up in Scotland several years ago by the Prince, have been impressed by

Ms Stewart's flair and business acumen.

She received a loan from the trust three years ago to allow her to

establish her own photography business, based at the Stirling Enterprise

Park. Her talents have already resulted in the steady expansion of the

business.

She said: ''I have now taken on another photographer and two people to

handle the administrative side of things.''

While looking forward to her royal appointment, Aileen is reluctantly

having to accept one rule -- to leave the camera at home. ''Theyhave

ordered me to take the night off,'' she said.