As I was going by Charing Cross is a nursery rhyme. The lyrics are:

As I was going by Charing Cross,
I saw a black man upon a black horse;
They told me it was King Charles the First -
Oh dear, my heart was ready to burst!

The origin of the children's nursery rhyme 'As I was going by Charing Cross' stems from the public execution of King Charles I of England. The charge was a follows:

"out of a wicked design to erect and uphold in himself an unlimited and tyrannical power to rule according to his will, and to overthrow the rights and liberties of the people of England."

There had been no clear support by the people to try Charles and the man who was to execute Charles refused to do it, as did others. Eventually an executioner was found who was paid an enormous sum of £100. The executioner insisted on wearing a mask so that no one would ever know who he was. King Charles was executed on a scaffold outside the Banqueting House in Whitehall, London at 2:00 o’clock in the afternoon on Tuesday 30th of January in 1648. The scaffold was hung round with black and the floor covered with black and the Axe and block laid in the middle of the scaffold. Next to the block and ax were "Hooks and Staples to drag the king to Execution, should he make any sort of Resistance - he did not. Troops of horse were placed on the one side of the scaffold towards Kings Street and on the other side towards Charing Cross where multitudes of people gathered to witness the event. When he was beheaded a large groan went up throughout the crowd '...the execution was met with 'such a groan as I have never heard before, and desire I may never hear again' reflecting the last line of the nursery rhyme - 'Oh dear, my heart was ready to burst'.