The Earl of Strathmore who admitted sexually assaulting a woman at his ancestral home, is due to be sentenced on Tuesday.
Simon Bowes-Lyon, 34, a relative of the Queen, admitted to attacking a woman at Glamis Castle, Angus, in February last year.
Bowes-Lyon, who is the son of a cousin of the Queen, is up for sentencing at Dundee Sheriff Court.
Previously, the court heard that the incident happened in a bedroom at the castle.
In a statement issued outside court, Bowes-Lyon said: “I am greatly ashamed of my actions which have caused such distress to a guest in my home. When I realised what I had done I apologised quickly to the woman concerned.
“I apologise wholeheartedly again today. I am deeply sorry for my behaviour and the anguish it has caused.
“Clearly, I had drunk to excess on the night of the incident. As someone who is only too well aware of the damage that alcohol can cause, I should have known better. I recognise, in any event, that alcohol is no excuse for my behaviour.
“I did not think I was capable of behaving the way I did but have had to face up to it and take responsibility. Over the last year this has involved seeking and receiving professional help as well as agreeing to plead guilty as quickly as possible.
“My apologies go, above all, to the woman concerned but I would also like to apologise to family, friends and colleagues for the distress I have caused them.”
Glamis Castle is the seat of the Earls of Strathmore and Kinghorne, the family which the late Queen Mother was part of.