Kate Middleton has made a smooth transition from a shy commoner marrying into the British royal family to the perfect future Queen consort of the UK in the past decade, and has even left Queen Elizabeth II impressed with her transformation.

According to a report in Us Weekly, the Queen is relieved after realising that her granddaughter-in-law can effectively secure the future of the British monarchy after her. A source told the outlet, "Over time, Kate has proved to Elizabeth that she can be trusted and they've developed a great relationship. Elizabeth feels confident that Kate will make a great queen."

Kate started her journey as a senior British royal in April 2011, upon her wedding to Prince William, second-in-line to the British throne. The Duchess of Cambridge, who was described as professional but reserved in her early years, is now being hailed as a "royal rockstar" following her confident appearances in recent months.

The insider said that though it took her 10 years to conquer the feeling of being "uneasy in the spotlight," she has now transformed into a "fearless" public figure who also "knows (the protocols) like the back of her hand."

Meanwhile, her relationship with the reigning Queen has also made big strides. Though they never had a poor association to begin with, Kate reportedly felt "nervous" being around the monarch in her early days as a royal and "was so desperate to impress." But now she and William have been in regular contact with the Queen to learn more about their future roles, and have left the 95-year-old feeling "confident that they cross all the boxes to rule."

When William takes over the British throne after his father Prince Charles, Kate will be named the Queen Consort, unlike her predecessor Duchess Camilla who will reportedly be called the Princess Consort. Kate is "slightly nervous" about the major responsibility that comes with being the monarch's spouse, but has gained a lot of confidence as well.

The source explained, "She's always up for a challenge, believes in herself and feels that she has developed the wisdom, courage and strength to be a success."

Apart from serving the country as the monarch couple, Kate and William will also have the responsibility to prepare their eldest child Prince George for his future as the King. A source previously said that they are "nervous about what the future holds for George," and have been "cautious" about putting the eight-year-old and his younger siblings Princess Charlotte, 6, and Prince Louis, 3, in the spotlight.

queen Elizabeth II longest reign
13 June 2012: Kate Middleton laughs as the Queen gestures while they watch part of a children's sports event during a visit to Vernon Park in Nottingham Phil Noble/Reuters