China's then top leader Deng Xiaoping, left, meets with visiting British Queen Elizabeth II in Beijing during the queen's trip to China in October 1986. The Queen became the first British monarch ever to visit China when she paid a state visit to the country in 1986. PROVIDED TO CHINA DAILY

Queen Elizabeth II, who 30 years ago became the first British monarch to visit China, turns 90 on Thursday, and a series of public celebrations are getting underway to pay tribute to the country's longest-serving sovereign.

She met Chinese leader Deng Xiaoping during her visit to Beijing in October 1986, less than two years after China and the UK agreed on the future of Hong Kong and at a time of increasing British-Chinese trade.

Over the next 30 years, the Queen welcomed three top Chinese leaders, including former presidents Jiang Zemin and Hu Jintao and current President Xi Jinping. On each occasion, she invited them to stay as her guest at Buckingham Palace, seen as the highest honor under royal protocol.

"I have seen for myself how highly Her Majesty values UK-China relations and the role that she can play in furthering friendship between the two countries," Sir Christopher Hum, former British ambassador to China, told China Daily in London.

President Xi, who heralded a golden era between China and UK after his state visit to the UK last year, sent birthday greetings to the queen when he met with her son Prince Andrew in April in Beijing.

"I understand that ... the United Kingdom will soon be celebrating the 90th birthday of Her Majesty Queen Elizabeth II and also the 95th ... of his Royal Highness the Duke of Edinburgh," Xi said. "I'd like to wish them good health and longevity."

Queen Elizabeth famously has two birthdays: her actual birthday on April 21 and her official birthday, which is in June.

Britain's Queen Elizabeth and President Xi Jinping are driven by carriage along The Mall to Buckingham Palace in London, Oct 20, 2015.[Photo by Wu Zhiyi/China Daily]