Prince William might be the key to confirming Kate Middleton’s fourth pregnancy.

While speaking with Express, body language expert Judi James said that Middleton is known for dropping clues of her pregnancy.

For instance, she usually cradles her growing baby bump before the palace confirms that she’s expecting. But it is her husband that could provide clues to her pregnancy.

James said that the Duke of Cambridge’s facial expression will be a massive giveaway. After all, Prince William’s face is very expressive, and it’s a struggle for him to contain his excitement.

“Unlike his dad, he might manage to mask negatives like anger or frustration, but watch out for a lot of suppressed smiling if/when he is sitting on a fourth baby secret. Trying to suppress a smile leads to a softened eye expression and narrowing and crinkling of the eyes, plus a pushing together of the lips, but the smile breaking out at the corners,” she said.

James also said that Prince William and Prince Harry are known for using subconscious mimicry rituals that gave clues regarding their wives’ pregnancies. At one point, the royal siblings also placed their hands on their belly, which is also what their wives did.

“Sadly for Kate, the acute sickness she suffers tends to provide the most reliable clue if/when her diary is emptied of all official functions, so we might need to look at the timing and context as well as the behavior of some of the other royals to spot any subtle or less than subtle hints that baby number four is on the way,” James said.

Following a recent engagement, Prince William and Middleton showed the public how happy they are in their marriage. James said that this could also signal that they are already preparing to become parents of four.

“The couple’s strong mirroring traits have always given clues of a like-minded relationship but here they seem happy to use many more tie-sign gestures than usual, keeping in communication with and enjoying one another’s company via glances, shared smiles and actual touches to allow us to glimpse more open affection and closeness,” she said.

However, Prince William and Middleton have not yet announced the latter’s pregnancy. As such, it is important to note that James’ predictions are just based on her own observations.