Legendary rocker Sir Rod Stewart has left his fans gob-smacked after sharing an update alongside his three youngest sons. The Maggie May singer took to Instagram on Tuesday night to celebrate his son Liam’s, 29, ice hockey triumph with his team MK Lightning. The Milton Keynes-based ice hockey team was crowned National Cup champions on Tuesday night and Stewart was in attendance to cheer his son on. The 79-year-old wasn’t cheering solo, however, as sons Alastair, 18, and Aiden, 13, also joined him to support their brother’s team. Celebrating MK Lightning’s triumph, Stewart and his three boys st…