King Charles III left fans delighted with his major surprise on Prince Harry's big day as he broke the cover with in a cheerful appearance.

King Charles was all smiles and in good spirit as he waved to crowds moments before Harry attended his Invictus Games thanksgiving service at St Paul's cathedral in London.

The cancer-stricken King looked fit and healthy sound during his latest outing. 

The King's appearance at the time of Harry's event seems to be another blow to the Duke of Sussex as the 75-year-old monarch has no plans to meet his youngest son Harry who is in the capital to celebrate a milestone for the Invictus Games Foundation.

The King's medical team has already given him green light from to attend public-facing duties.

The King was seen leaving Clarence House on Wednesday at the time when Harry was attending the celebrations of his milestone.

Harry has been open about the fact that his relationship with Charles and William has been strained in recent years. The last time he saw his father was shortly after the monarch had been diagnosed with cancer when he rushed back to see him.

Royal expert and author Tom Quinn, Speaking to the Mirror: "Although the statement about his father being too busy to see him makes it look as if Charles is refusing to see his son, the truth is that Harry himself is just as reluctant to see his father. The relationship is just too toxic."