Britney Spears is back on Instagram three weeks after her DUI arrest. Spears, 44, took to the social media site on Friday, March 27, with a video featuring her son Jayden, 19, whom she shares with ex-husband Kevin Federline. (The pair are also parents of son Sean Preston, 20.) The montage featured several clips of the mother-son duo posing in mirrors together. In one part, Spears energetically jumped beside Jayden before telling him, "I'm being very composed." In the caption, Spears added, "Thank you guys for all your support ...