Prince William and Tom Parker Bowles will be witnesses at their parents' wedding, British royal officials said.

The two sons will be among 30 people attending Prince Charles and Camilla Parker Bowles' civil marriage ceremony April 8 at Windsor town hall. Charles' younger son, Prince Harry, and three siblings -- Princes Andrew and Edward and Princess Anne -- also will attend, Charles' office said Wednesday.

Queen Elizabeth II will be absent at the wedding but will attend a blessing ceremony afterward at nearby Windsor Castle. The blessing ceremony will be televised, but the marriage itself will not.

Clarence House announced last month that the 56-year-old heir to the British throne would wed his longtime lover Parker Bowles, 57.

It is unprecedented for an heir to the throne to marry in a civil ceremony, but the Church of England -- which Charles will head when he becomes king -- has qualms about remarriage for divorcees.

Both the Prince of Wales and Parker Bowles were divorced, and her husband is still living. Charles' first wife, Princess Diana, died in 1997 in a Paris car crash.

The civil ceremony is expected to last about 20 minutes. Clarence House said the couple would make the short drive from Windsor Castle to the wedding venue in a 1962 Rolls-Royce Phantom V previously used by the late Queen Mother Elizabeth.

Asked whether Prince William was happy to be performing the role of witness, a spokesman for the prince said: "Very much so."

Clair Williams, who conducts about 100 weddings a year, also said she was looking forward to officiating on April 8.

Welcoming the announcement from Clarence House that she would conduct the ceremony, she said: "I am absolutely delighted and honored to be asked to conduct this historic and absolutely unique ceremony.