Dave Quinn and Simon Perry
April 25, 2018 08:22 AM

The new prince may only be three days old, but he’s already “behaving himself” and sleeping “well.”

On Wednesday, new dad-of-three Prince William stepped out to attend an Anzac Day Service of Commemoration and Thanksgiving at Westminster Abbey alongside brother Prince Harry and sister-in-law to-be Meghan Markle. And as he arrived, he couldn’t help but gush about the newest addition to he and wife Kate Middleton‘s family. 

Asked how the baby boy is doing, William, 35, said, “Very well, thanks.”

He added that everyone is “in good form, luckily” and said his new son — whose name has yet to be released — is already sleeping well.

“Sleeping’s going reasonably well so far, so he’s behaving himself which is good,” said William.

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William and Princess Kate’s baby boy was born in London on Monday at 11:01 a.m. local time. He weighed at 8 lbs., 7 oz.

Mom and dad — who debuted their son to the world just seven hours after Kate gave birth — have already returned home to Kensington Palace, where they are beginning life as a family of five.

“It completes them,” royal biographer Ingrid Seward told PEOPLE in this week’s cover story. A friend of the couple noted that Kate, 36, “is one of three siblings, and it’s a good family size. Boy-girl-boy is pretty cool as well.”

RELATED: See the New Royal Baby Prince from Every Angle!

For much more on the new royal family of five, pick up this week’s issue of PEOPLE, on newsstands Friday

Parenthood, the friend added, “suits them really well. They are enjoying it and are very happy.”

Big brother Prince George, 4, and big sister Princess Charlotte, who turns 3 on May 2, “are so excited,” said another friend. “Kate’s worried that Charlotte will feel it the hardest as the youngest, but she’s such a confident little girl and growing up so fast, Kate is hoping she will adjust.”

RELATED VIDEO: Prince George and Princess Charlotte Visit Royal Baby in the Hospital

Meanwhile, Anzac Day falls every year on April 25 — the anniversary of the landings in the Dardanelles of 1915.

Though originally devised to honor the members of the Australian and New Zealand Army Corps who fought against the Ottoman Empire at Gallipoli in World War I, the day has now become a national day of remembrance for all deceased service members and veterans throughout Australia and New Zealand.

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