2x2 mixed ANOVA interaction - do I analyse simple main effects?

#1
I've conducted a 2x2 mixed factorial ANOVA:
IV1 - repeated measures (control vs. experimental)
IV2 - between groups (I counter-balanced the order so the groups are Order 1 and Order 2)

There is a significant interaction between the two IVs. I can see from a graph where the interaction is.

My question is this: Do I need to do an analysis of simple effects when it's a 2x2 design? When I do one-way ANOVAs, there is a significant difference between control and experimental for order 1 but not order 2. This difference is significant after a Tukey HSD analysis. But do I report the results of the one way ANOVAs (four in total) or the Tukey HSD results, or is stating that there's an interaction enough?