Police have been alerted after an angry pensioner threatened to ruin the wedding of an aristocratic friend of Prince William and Kate Middleton.
Michael McNamara, 71, has vowed to disrupt the wedding service of Lady Katie Percy, the eldest daughter of the Duke and Duchess of Northumberland.
The pensioner wrote to Lady Katie to say he and a gang of relatives would turn up at the event.
Mr McNamara, who in recent years changed his name by Deed Poll to Michael "Bastard" McNamara, said he was warned he faced arrest if he caused trouble.
Lady Katie, 28, will marry financier Patrick Valentine, 30, in St Michael's Church, Alnwick, Northumberland, before a reception at Alnwick Castle. More than 300 guests are expected to attend the ceremony.
It is believed Mr McNamara developed a grudge against the Percy family following a dispute over the water supply at his home.
He has bombarded the Duke and Duchess, and Northumbria Police, with foul-mouthed and insulting postcards for many years.
He told The Journal in Newcastle: "I've sent postcards to the police all my life. The Duchess used to get one every year but I sent one to her and her daughter last Friday. The police just said 'How would you like it if they sent it to me?'
"I told them I was going to the wedding and they said that if I went I was going to get arrested. I said, 'I will see you at the wedding'."
A family spokesman denied speculation that Prince William and fiancee Kate Middleton will attend the service this Saturday, nine weeks before their own wedding at Westminster Abbey. It has been reported that Lady Katie and her new husband have been invited to the royal wedding.