Princess of Wales Kate Middleton was ‘exhausted’ after Trooping the Colour, her first public appearance since cancer diagnosis earlier this year, an insider has claimed.

Kate Middleton attended Trooping the Colour, King Charles official birthday celebrations, despite her cancer treatment last month.

Now, despite her radiant appearance at the event, an insider has told Life & Style, "Kate was exhausted afterward. It was a long day, and it took a lot out of her."

However, the source claimed Prince William was "very proud of Kate Middleton."

"Kate was nervous making her reappearance. She worried she would look tired or too thin at the parade, but she looked amazing. The supportive response Kate got boosted her confidence, and it was apparent", the source close to royal family said.

The insider added Kate Middleton’s ‘display of strength’ despite cancer battle proves she would make a ‘worthy queen’ one day when Prince William becomes King.

"She's a fighter, for herself, her family and her country."

Ahead of the royal event, Kate Middleton had issued an emotional statement saying “I am making good progress, but as anyone going through chemotherapy will know, there are good days and bad days.

“My treatment is ongoing and will be for a few more months.”