Stjerne represented Denmark at the 2012 World Men's Curling Championship in Basel, where Denmark finished outside of the playoffs. Later that year, he led Denmark to a 4th-place finish at the 2012 European Curling Championships. He followed this up by placing 4th at the 2013 Ford World Men's Curling Championship, and again finishing 4th at the 2013 European Curling Championships. Stjerne skipped Denmark at the 2014 Winter Olympics, leading the team to a 6th-place finish with a 4-5 record.