This never happened before

My family got two dogs almost a month ago, they are both 3 months and were siblings, today the boy Landon was playing and eating earlier today, was acting very normal. We let them go outside and 45 minutes later he was gone, he wouldn't move. His sister is sad. We didn't have both of them for long but we bonded with both of them incredibly fast. I'm so hurt. I don't understand what happened. We owned pets my whole life and we never had one that died out of nowhere...no symptoms at all. We're trying to give London (the girl ) a lot of love. (we know their names sound alike we couldn't decide) They did everything together and were very codependent. The girl is a anatolian Shepard and the boy Landon- that passed today was a Pyrenees Shepard (the lighter one). 🩷