Franklin Graham has said the Queen - a personal friend of his late father, the evangelist Billy Graham - will be "profoundly missed".
The Samaritan's Purse CEO said he was "deeply saddened" to hear about the death of the Queen on Thursday at the age of 96.
He called her a "true friend of the Christian faith" and "a symbol of stability and steadfastness for the United Kingdom for 70 years".
Asking people to join him in praying for the royal family and the people of the UK, he said, "I will always appreciate her example of leadership and her life of integrity."
He continued his message by saying that he was "especially grateful" for the friendship between his father and the Queen, who he said had met more than a dozen times, including during several visits to Buckingham Palace where she had been "a gracious host".
"He cherished their friendship that was built on a shared love for Jesus Christ and belief in God's Word," he said.
"My father said he found Queen Elizabeth 'to be a woman of rare modesty and character,' and made a pledge to pray for her and her family every day.
"He also appreciated how she often talked about Jesus Christ during her public addresses—there was never any question about where she placed her faith."
He concluded his message: "The Queen was a friend to my father, but more importantly, she was a true friend of the Christian faith. She will be profoundly missed."
Billy Graham was a much-loved evangelist and spiritual adviser to American presidents who died in 2018. During his lifetime, he visited the UK many times for evangelistic crusades.
He preached several times in the Queen's private chapel and received an honorary knighthood in 2001. The Queen and Graham remained lifelong friends.