A handwritten card accompanied the wreath of flowers placed on top of the late Queen's coffin during her funeral.
As the coffin traveled from Westminster Hall to Westminster Abbey for the service, and departed again to Wellington Arch to be transferred into a hearse for its journey to Windsor Castle, viewers clocked the personal message.
The note, written by King Charles to his mother, reads: "In loving and devoted memory. Charles R."
The 'R' stands for rex, Latin for 'king', which he inherited after Queen Elizabeth II's death.
During her reign, the 'R' used next to her name stood for regina, Latin for 'queen'.
This gesture is reminiscent of when the Queen wrote a note for the late Prince Philip's coffin. She signed a similar message with 'Lilibet', the childhood nickname used by her husband.
The note from Charles to the late monarch was carefully placed among a wreath of flowers, in shades of gold, pink and deep burgundy, with touches of white, which included another tribute.
As requested by him, it was made of flowers cut from the gardens of Buckingham Palace, Clarence House and Highgrove House, with symbolic foliage.
Watch: Queen's children and grandchildren walk behind coffin at funeral
Rosemary was used for remembrance, while myrtle was used as the ancient symbol of a happy marriage, cut from a plant grown from the sprig of myrtle in the late Queen's wedding bouquet in 1947. English oak also symbolised the strength of love.
The note nestled in flowers sat behind by the Imperial State Crown, placed on a purple velvet cushion.