Prince Harry Makes a Surprise Appearance Alongside Kate Middleton Days Before Welcoming Baby

Stephanie Petit

Kate Middleton had a special guest while returning to royal duty: her brother-in-law (and soon-to-be first-time father), Prince Harry!

While it was previously announced that the royal mother of three, 37, would step out on Thursday to honor fallen Australian and New Zealand veterans during the annual Anzac Day Service of Commemoration and Thanksgiving at Westminster Abbey – the very spot where she and Prince William tied the knot nearly eight years ago, on April 29, 2011 – it was a surprise to see Harry join her. After all, he and Meghan Markle are expecting their first child any day now!

A royal source tells PEOPLE that Harry hoped to participate in the service, yet precautions were made in case the baby arrived.

Harry is “pleased he can attend today’s service, as planned,” the insider says. “With their baby due, his name was not printed in the program in case he was unable to do so.”

Kate Middleton and Prince Harry | Samir Hussein/WireImage
Kate Middleton and Prince Harry | DANIEL LEAL-OLIVAS/AFP/Getty Images

The day of remembrance commemorates the first major battle involving Australian and New Zealand forces during World War I. It has been honored in London since the first anniversary of the Anzac landings at Gallipoli in 1916, when King George V attended a service at Westminster Abbey.

Despite the solemn occasion, the pair were all smiles as they headed inside.

Kate Middleton | Tim Rooke/REX/Shutterstock

Kate is known to love recycling her favorite outfits, but she stepped out in something new for Thursday’s outing. She wore a bespoke teal coat dress by Catherine Walker & Co, featuring three large buttons and a raised neckline.

She paired the ensemble with a statement headpiece, matching the coat’s color with an array of feathers organized in an ornate pattern. The royal carried a green clutch and wore matching heels to complete the look, along with blue topaz Kiki Classic earrings and an Eden necklace in white gold.

Kate Middleton | Tim Rooke/REX/Shutterstock

Harry, a veteran himself, decked out his suit and tie with medals. Both royals wore red poppy pins, a symbol used since 1921 to commemorate military members who have died in war.

Prince Harry | Andrew Matthews/PA Images via Getty Images

The Duke of Gloucester, a paternal cousin of the Queen’s and currently 26th in the line of succession to the British throne, was also in attendance.

Prince Harry, the Duke of Gloucester and Kate Middleton | REX/Shutterstock

Meanwhile, Kate’s husband Prince William arrived in New Zealand on April 25. He began his trip in Auckland attending services for the day of remembrance. (The trip has some wondering if William will miss the birth of Prince Harry and Meghan’s first child.)

Prince William, Meghan Markle and Prince Harry attend an Anzac Day service in 2018 | Eddie Mulholland - WPA Pool/Getty Images)
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Last year, Kate missed the Anzac Day service – but for a good reason. The day of remembrance came just two days after she welcomed her third child, Prince Louis.

Prince William attended the solemn service with Meghan and Harry. However, the royal dad couldn’t hide the effects of having a newborn at home, closing his eyes and appearing to momentarily doze off during the ceremony.