Duchess Kate shares Prince Louis' favourite song

Kate has shared what Prince Louis' favourite song is. Photo / Getty Images

Catherine, Duchess of Cambridge, has revealed what Prince Louis' favourite song is, and it's adorable.

The Duchess held a reception last night at Buckingham Palace celebrating the 25th anniversary of mental health charity Place2Be.

According to the Sun, the royal mum spoke to students from the New North Academy in Islington and Salusbury Primary School in North West London who had gathered to perform for her.

Kate, 38, later discovered that it was the birthday of two of the pupils and wished them well, joking that she was the one who should be singing to them.

She then revealed that Happy Birthday was one of Prince Louis' favourite songs, although he won't hear it until he turns 2 on April 23.

The young prince's favourite tune is the Happy Birthday song. Photo / Getty Images

The kids had written a special song for the occasion and according to Hello!, the Duchess offered them some words of encouragement.

"You've written it, especially for tonight? Thank you so much! What a treat for me," she said.

She's been the patron for the charity since 2013 and spoke to charity members about the pride she feels.

Earlier in the week, Kate appeared with William at Westminster Abbey for the annual Commonwealth Day service.

It was also Harry and Meghan's last engagement as royals before Megxit officially takes effect.