London (CNN) -- Sixty years ago Monday, a 25-year-old woman visiting a remote part of Kenya got a message that her father had died. 

She cut her trip short and flew home to London. Prime Minister Winston Churchill met her at the airport -- because with her father dead, she had become Queen Elizabeth II. 

Celebrations of her Diamond Jubilee, marking six decades on the throne, officially begin Monday and continue through June, when London will mark the anniversary of her coronation with festivities including up to 1,000 boats sailing up the River Thames. 

On Monday, the queen thanked the public "for the wonderful support and encouragement that you have given to me and (husband) Prince Philip over these years." 

She said in the open letter that she planned to "dedicate myself anew to your service." 

She called on people to "give thanks for the great advances that have been made since 1952 and to look forward to the future with clear head and warm heart" in a brief letter that she signed simply "Elizabeth R." 

She was honored with a 41-gun salute in London's Hyde Park Monday, and a 21-gun salute in Edinburgh, Scotland. 

Two new photographs of the queen were released Monday as part of the Diamond Jubilee celebrations, showing her wearing a necklace worn by Queen Victoria in her own Diamond Jubilee portrait in 1897. 

She is the oldest British monarch in history, but has not yet passed her great-great-grandmother Victoria as the longest-reigning one. 

Elizabeth II was not in line to the throne when she was born April 21, 1926. But the fate of Lilibet, as she was known to her friends, changed when her uncle Edward abdicated the thone to marry Wallis Simpson, an American divorcee. 
what is one festivity that will take place to celebrate?
festivities including up to 1,000 boats sailing up the River Thames.