Armstrong races with Chip Ganassi Racing, currently 11th in the championship, and will be competing in the historic Indy 500 event this weekend.
The physio frequently posts pictures of the pair together on social media, whether that is in the race paddock or enjoying food together.
In a recent interview with the Associated Press, Armstrong revealed how important Cullen has been to his racing career, and that the pair now live together.
Armstrong described the biggest issue in living with Cullen is that he hears her leave very early for a morning run, and “the two then meet in the kitchen for coffee" when she returns.