Britain's Prince William (L) and his fiancee Kate Middleton, leave after a visit to Belfast City Hall in Belfast, Northern Ireland, on March 8, 2011. Prince William and his bride-to-be Kate Middleton arrived in Belfast on Tuesday for a one-day visit, under the watchful eye of armed police on the surrounding rooftops. AFP PHOTO/PAUL ELLIS

Kate Middleton, (L) and Britain's Prince William are pictured during a visit to Belfast City Hall in Belfast, Northern Ireland, on March 8, 2011. Prince William and his bride-to-be Kate Middleton arrived in Belfast on Tuesday for a one-day visit, under the watchful eye of armed police on the surrounding rooftops. AFP PHOTO/NIALL CARSON/POOL

Britain's Prince William (L) accompanied by his fiancee Kate Middleton, watch a tug of war match during a visit to Greenmount Agricultural College near Belfast, Northern Ireland, on March 8, 2011. Prince William and his bride-to-be Kate Middleton arrived in Belfast on Tuesday for a one-day visit, under the watchful eye of armed police on the surrounding rooftops. AFP PHOTO/PAUL ELLIS

Britain's Prince William (R) accompanied by his fiancee Kate Middleton, watch a tug of war match during a visit to Greenmount Agricultural College near Belfast, Northern Ireland, on March 8, 2011. Prince William and his bride-to-be Kate Middleton arrived in Belfast on Tuesday for a one-day visit, under the watchful eye of armed police on the surrounding rooftops. AFP PHOTO/PAUL ELLIS

Britain's Prince William (L) and his bride-to-be Kate Middleton arrive at George Best Belfast City Airport for a a one-day visit to Northern Ireland, on March 8, 2011. Britain's Prince William and his bride-to-be Kate Middleton arrived in Belfast on Tuesday for a one-day visit, under the watchful eye of armed police on the surrounding rooftops. It is the couple's first official visit to Northern Ireland, and they were greeted enthusiastically by a small crowd who had gathered in the grounds of City Hall for a glimpse of the royal pair. AFP PHOTO/Stephen Davison/POOL

Prince William (L) and his fiancee Kate Middleton wave as they pass St Salvator's halls during a visit to the University of St Andrews in Scotland on February 25, 2011. During the visit they viewed the surviving Papal Bull (the university's founding document), unveiled a plaque, and met a selection of the University's current staff and students to mark the start of the Anniversary. Prince William and Kate Middleton attended the university as students from 2001 to 2005 and began their romance in St Andrews.2011. AFP PHOTO/WPA POOL/ANDREW MILLIGAN

Prince William (L) and his fiancee Kate Middleton pass St Salvator's halls during a visit to the University of St Andrews in Scotland on February 25, 2011. During the visit they viewed the surviving Papal Bull (the university's founding document), unveiled a plaque, and met a selection of the University's current staff and students to mark the start of the Anniversary. Prince William and Kate Middleton attended the university as students from 2001 to 2005 and began their romance in St Andrews.2011. AFP PHOTO/WPA POOL/ANDREW MILLIGAN

TOPSHOTS Prince William (L) and his fiancee Kate Middleton smile during a visit to the University of St Andrews in Scotland on February 25, 2011. During the visit they viewed the surviving Papal Bull (the university's founding document), unveiled a plaque, and met a selection of the University's current staff and students to mark the start of the Anniversary. Prince William and Kate Middleton attended the university as students from 2001 to 2005 and began their romance in St Andrews.2011. AFP PHOTO/WPA POOL/ANDREW MILLIGAN

Britain's Prince William and his fiancee Kate Middleton exchanges glances, during a visit to the University of St. Andrews, in St. Andrews, Scotland, where they first met, Friday Feb. 25, 2011. The couple, who both graduated from the university, are scheduled to marry on April 29, at London's Westminster Abbey.(AP Photo/Danny Lawson, pool)

Britain's Prince William (R) and fiancee Kate Middleton arrive for a naming ceremony for the new Royal National Lifeboat Institution's (RNLI) Atlantic 85 lifeboat 'Hereford Endeavour' at the RNLI Lifeboat Station in Anglesey, near Bangor in Wales, on February 24, 2011. Kate Middleton got a taste of life as a working royal Thursday when she and Prince William dedicated a lifeboat in their first official appearance since their engagement. Hundreds of people cheered as the smiling 29-year-old princess-to-be poured a bottle of champagne over the vessel in a dedication service at the lifeboat station Trearddur Bay on Anglesey, northwest Wales. AFP PHOTO/Andrew Yates

Britain's Prince William and his fiancee Kate Middleton pose for photographers during a photocall to mark their engagement, in the State Rooms of St James's Palace, central London on November 16, 2010. Prince William will marry his girlfriend Kate Middleton next year, the royal family said Tuesday, in the biggest royal wedding in Britain since his parents Charles and Diana married in 1981. The announcement ended feverish speculation about when the second-in-line to the throne would wed, after a romance that has already lasted nearly eight years. AFP PHOTO / BEN STANSALL

Britain's Prince William (R) and his fiancee Kate Middleton pose for photographers during a photocall to mark their engagement, in the State Rooms of St James's Palace, central London, on November 16, 2010. Prince William will marry his girlfriend Kate Middleton next year, the royal family said Tuesday, in the biggest royal wedding in Britain since his parents Charles and Diana married in 1981. The announcement ended feverish speculation about when the second-in-line to the throne would wed, after a romance that has already lasted nearly eight years. AFP PHOTO/BEN STANSALL

Britain's Prince William and his fiancee Kate Middleton, pose for photographers during a photocall to mark their engagement, in the State Rooms of St James's Palace, central London on November 16, 2010. Britain's Prince William has given his fiancee Kate Middleton the engagement ring that belonged to his late mother Diana, Princess of Wales, Clarence House said Tuesday. The blue sapphire and diamond ring was given to Diana by William's father, Prince Charles, when they became engaged in February 1981. Charles and Diana divorced in 1996 and she was killed in a car crash in Paris the following year. AFP PHOTO / BEN STANSALL

Britain's Prince William and his fiancee Kate Middleton react as they pose for photographers during a photocall to mark their engagement, in the State Rooms of St James's Palace, central London on November 16, 2010. Britain's Prince William has given his fiancee Kate Middleton the engagement ring that belonged to his late mother Diana, Princess of Wales, Clarence House said Tuesday. The blue sapphire and diamond ring was given to Diana by William's father, Prince Charles, when they became engaged in February 1981. Charles and Diana divorced in 1996 and she was killed in a car crash in Paris the following year. AFP PHOTO / BEN STANSALL

Britain's Prince William and his fiancee Kate Middleton pose for photographers during a photocall to mark their engagement, in the State Rooms of St James's Palace, central London on November 16, 2010. Britain's Prince William has given his fiancee Kate Middleton the engagement ring that belonged to his late mother Diana, Princess of Wales, Clarence House said Tuesday. The blue sapphire and diamond ring was given to Diana by William's father, Prince Charles, when they became engaged in February 1981. Charles and Diana divorced in 1996 and she was killed in a car crash in Paris the following year. AFP PHOTO / BEN STANSALL

FILE - This is a Tuesday Nov. 16, 2010, file photo of Britain's Prince William and his fiancee Kate Middleton arrive for a media photocall, media at St. James's Palace in London, Tuesday Nov. 16, 2010, after they announced their engagement. The couple are to wed in 2011. The wedding of Britain's Prince William and Kate Middleton is in 100 days time on April 29, 2011. (AP Photo/Sang Tan, File)

(FILES) A file photo taken on April 11, 2008 shows Britain's Prince William and his girlfriend Kate Middleton after his graduation ceremony at RAF Cranwell air base in Lincolnshire. Britain's Prince William, the second in line to the throne, will marry his long-term girlfriend Kate Middleton next year, Clarence House said Tuesday. William, 28, the eldest son of heir to the throne Prince Charles and the late Princess Diana, and Middleton, also 28, became engaged in October while on holiday in Kenya, it said in a statement. AFP PHOTO/MICHAEL DUNLEA/POOL/FILES