Paul McCartney has announced the release of ‘Grandude’s Green Submarine’ – his second picture book.A direct sequel to 2019’s ‘Hey Grandude’, the book is set for release on September 2 and continues the adventure of the eponymous grandfather and his grandchildren as they set off on a quest to find their music-loving grandmother, Nandude.McCartney previously explained that the lead character’s name is taken directly from the nickname that his grandchildren are known to call him.‘I’m really happy