The card, which has black edges, reads: “In memory of His Royal Highness Prince Philip, Duke of Edinburgh – 1921 – 2021”.
Inside, the card includes a picture of Prince Philip, smiling as he looks away from the camera lens.
On the third page of the card, the couple shared a message under the black crest of their household.
It reads: “Thank you for your kind message of condolence.
“We are extremely grateful for your thoughtfulness in writing at this sad time.”
The message was signed off with their full titles: TRH The Earl and Countess of Wessex and Forfar.
While Sophie and Edward became Earl and Countess of Wessex on their wedding day in 1999, the Earldom of Forfar was awarded to them by the Queen on the prince’s 55th birthday.
Prince Edward will become the next Duke of Edinburgh when Prince Charles’s reign begins, as stated by Buckingham Palace ahead of the Wessexes’ nuptials.
After the death of Prince Philip, his royal title was automatically passed on to his firstborn Prince Charles.
However, upon ascending to the throne, all the titles bore by the Prince of Wales will merge into the Crown and cease to exist.
Therefore, they will be made once again available to be granted to other members of the family.
Prince Edward worked closely alongside his father on the Duke of Edinburgh Award scheme and was a trustee and chairman of the International Duke of Edinburgh Award.
As the future recipient of the Duke of Edinburgh title, he will no doubt continue to tirelessly work on the scheme.
Prince Edward and Sophie have been prominent figures during the period of royal mourning.
The day after Prince Philip died, the couple was pictured driving into Windsor Castle to support the grieving Queen.
Sophie also spoke to the press to reassure the public Prince Philip died peacefully.
She said: “It was right for him. It was so gentle. It was just like somebody took him by the hand and off he went.”
She continued: “Very, very peaceful and that’s all you want for somebody, isn’t it?
“So, I think it’s so much easier for the person that goes than the people that are left behind.”
Prince Edward, Sophie and their daughter Lady Louise were also seen looking at tributes left by royal fans outside the gates of Windsor Castle.
Again, mother and daughter were seen leaving the castle on April 16, where they likely supported the monarch during a difficult time.
Prince Philip died during the morning of April 9 at Windsor Castle.
His funeral was held on the following week, on April 17, at St George’s Chapel, following a moving procession started at the castle.