Prince William and Duchess Catherine. Picture: Instagram

Duchess Catherine visited West Ham football stadium with her husband Prince William and his brother Prince Harry.

The 35-year-old royal - who is three months pregnant with her third child - returned to her duties this week following two months off due to severe morning sickness, and decided to join her husband Prince William and his brother Prince Harry at the ground for the graduation ceremony of more than 150 sports coaching apprentices.

READ: Prince William and Catherine expecting baby in April

A source told HELLO! magazine: "She's better and is keen to do as much as she can. But she's taking it day-to-day in deciding what she can do."

The brunette beauty - who concealed her tiny bump underneath a blue suit - appeared to be in good spirits as she spoke with the young people who had completed the Coach Core scheme, which is designed to teach apprentices, aged between 16 and 24, technical sports skills alongside coaching.

The royal trio were spotted watching some practical skills before they attended the graduation ceremony where Baroness Karren Brady, who is the vice-chairman of West Ham United, gave a speech alongside Coach Core chairman Ed Wray.

The Duchess' outing comes just days after Kensington Palace confirmed that she and William - who already have four-year-old son George and Charlotte, two, together - will welcome their third child into the world in April.

The statement said: "The Duke and Duchess of Cambridge are delighted to confirm they are expecting a baby in April 2018."

The new baby will be the fifth in line to the throne, with Prince Harry - the child's uncle - being pushed into sixth.

William, 35, and Catherine - previously known as Kate Middleton - will kick off an exciting year with an official royal tour of Norway and Sweden in early 2018.