Prince Louis called them out in a sweet Christmas note.

It’s almost the end of a “brutal” year for Kate Middleton, who stepped back from public duties and the spotlight while battling cancer. Before the Princess of Wales revealed that she was finished with chemotherapy in an emotional September video, she and Prince William reportedly “leaned on” two key family members to get them through the tough time.

Kate publicly announced her diagnosis in March, months after a scheduled abdominal procedure uncovered the presence of cancerous cells. As she withdrew from her normal schedule of royal engagements, Kate’s parents–Carole and Michael Middleton–stepped in to help her with her kids, Prince George, Princess Charlotte, and Prince Louis.

“I think a shout-out should also go to Carole and Michael Middleton, who have undoubtedly been a vital part of the family this year, both practically and emotionally,” former BBC royal correspondent Jennie Bond told OK! about making it through an “incredibly difficult year.”

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She explained that it was likely that “William and Catherine leaned on them very hard during their darkest days,” which was demonstrated in a sweet thank you note from Prince Louis from Kate’s Together at Christmas carol service this year.

Photographers caught a glance of the message, which read, “Thank you to granny and grandpa because they have played games with me.” Bond told OK!, “As we know from Louis’ card on the tree at the carol service, Granny and Grandpa are great playmates for their grandchildren and have put in more than a shift or two playing games with them.”

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The Wales family’s closeness with the Middletons was further demonstrated during the holidays, as Kate and William broke with royal protocol to hold their own Christmas party for Kate’s parents in attendance. Carol and Michael Middleton also subtly showed their support throughout the year by stepping in to make official appearances along with other members of the royal family when Kate was unable to join.

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In her first post-treatment message, Kate shared a clip of her playing cards with her parents while opening up about how the experience had made them all closer. “The last nine months have been incredibly tough for us as a family. Life as you know it can change in an instant and we have had to find a way to navigate the stormy waters and road unknown,” she began the clip.

“The cancer journey is complex, scary and unpredictable for everyone, especially those closest to you,” she continued. “This time has above all reminded William and me to reflect and be grateful for the simple yet important things in life, which so many of us often take for granted. Of simply loving and being loved.”