Music of the Kings and Queens
"I was glad" is traditionally sung in a Christian church as an anthem if a British Monarch has a Coronation (when they are officially crowned King or Queen). It has been set to music by different composers. This one is by Hubert Parry (1902) for King Edward VII – it was also sung at the wedding for William and Kate.
This is the footage from William and Kate's wedding. It is sung by the choir as she walks down the aisle.
This performance of the song it harder to hear as the commentator talks over it but watch from 22.40 mins and you will hear the same anthem, 'I was Glad'.