On Thursday, the world watched as an adorably-hesitant Prince George arrived to his first day of school at Thomas's Batersea. Though the four-year-old's father, Prince William, did an excellent job flying solo for the pivotal event, we couldn't help but feel the absence of mom, Kate Middleton.

Middleton, who is currently pregnant with the couple's third child, is once again suffering from hyperemesis gravidarum, an acute form of morning sickness, and was reportedly too ill to make it out for the young prince's big day.

"Kate watched the news from home," a source close to the royal couple told Us Weekly. "She was desperately sad that she couldn't make it but she is on firm bed rest now until she feels better."

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Understandably, watching their oldest child head off to school brought mixed feelings for the royal couple. "The first day of a child's school is always a bittersweet day for a mother," the insider added. "Both Kate and William are extremely proud of George and how well-behaved he was as he arrived, but it's also a little frightening to see him grow up this fast!"

Hang in there, Kate!