Catherine, 44, recently completed the gruelling endurance event, scaling three of the highest peaks in the UK within 24 hours, to spread her message about life during and after cancer.
Reacting to the photo of Catherine beaming with delight at the summit of Ben Nevis, James discreetly left two emojis - a mountain and a heart - under the portrait.
Camilla, 77, who is patron of the charity MDD, hosted the event at her London home, Clarence House, for supporters as well as some of the amazing canines themselves.
James Middleton opened up on how his dog Isla helped him recover from depression and 'saved his life' when he struggled to reveal his struggle to everyone around him.
One of the photos showed James planting a kiss on his wife Alizee's cheek during a hiking trip to the Lake District, accompanied by the couple's beloved dogs.
James Middleton, brother of Catherine, Princess of Wales, has shared previously unseen pictures from his wedding to Alizée Thévenet to mark the couple's fourth anniversary.