Kate Middleton is by her children's side: Prince George, Princess Charlotte and Prince Louis join their mother at Trooping the Colour
Prince Louis was pictured looking unimpressed as he joined his siblings and mother in a carriage during today's Trooping the colour.
The youngest of the Wales children, Louis, six, who is loved by many royal fans thanks to his expressive behaviour, appeared less than thrilled during the ride, at point knitting his brows as he stared out of the window, open-mouthed.
Another snap of the young prince showed him frowning, with his mouth down-turned.
Meanwhile, Prince George, 10, appeared typically composed, while Charlotte, nine, was snapped beaming as she looked out of the carriage window at the assembled crowds.
The children were accompanied by their mother Kate, 42, who has been receiving treatment for an undisclosed form of cancer since late February. Today marked her first public appearance in months.
Beaming Princess Charlotte couldn't help but smile as she appeared alongside her brother Prince George at today's Trooping the Colour
Kate beams as she accompanies her children in a carriage during today's procession (pictured L-R: Kate, Prince Louis, Princess Charlotte)
Prince Louis (left) pulls a face at the crowd as Princess Charlotte (right) looks regal as they join the parade
Prince Louis is pictured trying to open a window on a balcony on Horse Guards Parade next to the Duchess of Edinburgh
Another snap of the popular young Prince showed him grimacing as he rode to Buckingham Palace
Prince George, Princess Charlotte, Prince Louis and Kate at Trooping The Colour today
The royal was on hand to ensure her children could enjoy the family day out to celebrate their grandfather's birthday - her presence meant they didn't have to travel to the palace without an adult in their carriage.
Prince William took part in the parade on horseback, while his children appeared alongside their mother in a carriage.
After the Princess of Wales' carriage arrived at Buckingham Palace, she and her family stepped out, showing off their outfits.
The future Queen was the picture of elegance and grace as she donned a crisp white structured pencil dress which had a bow along the neckline. The designer is believed to be Jenny Packham - many of whose creations Kate has donned before.
The garment featured a monochrome belted band which sat on her waist and highlighted her sophisticated frame. Kate opted for a simple black clutch bag and classy pointed white heels, which tied the chic look together.
She wore her glossy brunette tresses in a stylish braided low-bun and completed the look with a coordinating hat by Philip Treacy, and her Cassandra Goad Cavolfiore pearl earrings, which retail for £5,620. She completed the look with her Irish Guards Regimental Brooch - a nod to her role as the regiment's honorary colonel.
Meanwhile, Prince George wore a navy suit with a crisp white shirt and royal blue tie, and a pair of black lace-up shoes. His younger brother Louis wore a navy blazer and shorts, with a white shirt and royal blue tie, and a pair of loafers.
Ahead of her appearance, the Princess penned a moving personal message thanking the public for their support over her cancer diagnosis and revealing she is looking forward to attending the traditional ceremonial day.
Back in March, the Princess disclosed she was undergoing 'preventative chemotherapy' for an undisclosed form of the disease says her treatment is ongoing and will be for several months to come.
The Princess of Wales is pictured with her three children, Prince Louis, Princess Charlotte and Prince George on a balcony on Horse Guards Parade
The Princess of Wales speaks with Prince Louis as they watch Trooping the Colour today
Prince Louis tries to open a window during Trooping the Colour today
Prince William and Kate attend Trooping the Colour at Buckingham Palace in London today
Members of the Royal Family watch the flypast from the Buckingham Palace balcony today
While she will not be returning to public duties full-time, she revealed that she does now feel well enough, however, to undertake a small number of public engagements in the coming months.
To mark the news Kensington Palace have also released a stunning new portrait of the princess taken at Windsor this week by Matt Porteous showing her looking well and in a reflective mood.
In her message the Princess says she has been 'blown away' by all the kind messages of support and encouragement over the last couple of months.
'It really has made the world of difference to William and me and has helped us both through some of the harder times,' she wrote.
Movingly she reveals she is making 'good progress', but adds: As anyone going through chemotherapy will know, there are good days and bad days. On those bad days you feel weak, tired and you have to give in to your body resting. But on the good days, when you feel stronger, you want to make the most of feeling well.'
The Princess of Wales leaves Buckingham Palace during Trooping the Colour in London today
Prince Louis at Trooping The Colour on Horse Guards Parade in London today
The Princess of Wales leaves Buckingham Palace during Trooping the Colour in London today
She added: 'My treatment is ongoing and will be for a few more months. On the days I feel well enough, it is a joy to engage with school life, spend personal time on the things that give me energy and positivity, as well as starting to do a little work from home.
'I'm looking forward to attending The King's Birthday Parade this weekend with my family and hope to join a few public engagements over the summer, but equally knowing I am not out of the woods yet.
'I am learning how to be patient, especially with uncertainty. Taking each day as it comes, listening to my body, and allowing myself to take this much needed time to heal.
Thank you so much for your continued understanding, and to all of you who have so bravely shared your stories with me.'
The Princess first announced that she had cancer on March 22.
The Princess of Wales leaves Buckingham Palace during Trooping the Colour in London today
Prince William, Prince Edward and Princess Anne on horseback at Trooping the Colour today
The Princess of Wales leaves Buckingham Palace during Trooping the Colour in London today
In a hugely moving video statement, recorded at Windsor, she revealed that she had been diagnosed following serious abdominal surgery in January and was already undergoing 'preventative' chemotherapy.
In a deeply personal, unprecedented and emotional video message filmed just two days earlier, Catherine revealed the news had come as a 'huge shock' and that she and William 'have been doing everything we can to process and manage this privately for the sake of our young family'.
'It has taken us time to explain everything to George, Charlotte and Louis in a way that is appropriate for them, and to reassure them that I am going to be ok,' she said.
'As I have said to them; I am well and getting stronger every day by focusing on the things that will help me heal; in my mind, body and spirits. Having William by my side is a great source of comfort and reassurance too. As is the love, support and kindness that has been shown by so many of you. It means so much to us both.'
Kensington Palace said at the time that it would not be sharing details of what kind of cancer the princess has, or what stage of cancer it is and asked people not to speculate.
At the time of her abdominal surgery in January, Kensington Palace said that it was non-cancerous. They confirmed again in March that is the case and that no tests had confirmed the presence of cancer. However post-operative tests subsequently found that cancer 'had been present'.
A week ago, the royal apologised for missing out on a key rehearsal for the event, writing a letter to the Irish Guards, saying: 'I hope I am able to represent you all very soon'.