Tesla Motors CEO Elon Musk attends the 'Goldenes Lenkrad' Award at Axel Springer Haus on November 8, 2016 in Berlin, Germany./Ashley St. Clair
Elon Musk is taking a major step in his legal battle against Ashley St. Clair. 
The Tesla CEO—who shares 16-month-old son Romulus with the influencer—announced his plans to file for full custody…