"And June is the month that's being batted around because it's the month that Prince William turns 29. ... That birthday date could be very significant," Nicholl added.
Within hours of the announcement, and Middleton's appearance wearing the late Princess Diana's famous sapphire-and-diamond engagement ring, orders for replicas exploded, crashing jewelry websites.
Tuesday's announcement was followed by visible sighs of relief from the happy couple, and the queen said she is "absolutely delighted" for the couple, Buckingham Palace said hours after the announcement.
Like the queen, Middletons' parents, Michael and Carole Middleton, said Tuesday they too were "absolutely delighted."
Eight years after the couple met, Prince William appeared with Middleton for the first time as an engaged couple Tuesday.
"The Prince of Wales is delighted to announce the engagement of Prince William to Miss Catherine Middleton," a statement from Clarence House early Tuesday read.
Prince William, 28, asked Middleton, also 28, to marry him while the two were on vacation in Kenya last month, the statement said.
The happy couple appeared for the first time for reporters arm-in-arm before a barrage of camera flashes, Middleton wearing the famous engagement ring worn by William's mother, the late Princess Diana.
"He's a true romantic and we had a wonderful holiday in Africa and it was out there in a very quiet lodge and it was very romantic and it was very personal time for both of us," Middleton said.
In an interview with Britain's ITV News' Tom Bradby, who told "GMA" the interview was "terrifying," Middleton said the proposal came as a surprise, despite years of public speculation that the couple would wed.
"We were out there with friends, so I really didn't expect it at all," Middleton said. "It was a total shock when it came. Very excited."
The announcement came to the elation of Britons, many of whom viewed the engagement as a seemingly inevitable yet unreachable moment. Within 25 minutes of the announcement's posting on the royal Facebook page, more than 1,400 people "liked" the news. The numbers have since increased.
"It's about time! Congrats," one commenter wrote, a sentiment echoed by hundreds of others.
The two met nearly a decade ago while students at the University of St. Andrews in Scotland. The relationship garnered some controversy because Middleton does not come from royalty and royals are generally expected to wed other aristocrats.
William said the two were friends for more than a year and lived as flatmates. "It blossomed from then on," he said. "We had lots of fun. ... Same interests. She has a really naughty sense of humor."
When asked why it took so long to propose, a beaming William quipped, "I also didn't realize it was a race, otherwise I probably would've been a lot quicker.
"We have a great fun time together," the prince told reporters. As for the ring, William said, it, like Kate, was very special to him.
"Well as you may recognize now, it's my mother's engagement ring and it's very special to me, as Kate is very special to me now as well. It was only right the two were put together," William said. "It was my way of making sure mother didn't miss out on today and the excitement and the fact that we're going to spend the rest of our lives together."