  We present and discuss the UV/optical photometric light curves and absolute
magnitudes of the Type Ia supernova (SN) 2011de from the Swift
Ultraviolet/Optical Telescope. We find it to be the UV brightest SN Ia yet
observed--more than a factor of ten brighter than normal SNe Ia in the
mid-ultraviolet. This object is an extreme example of the differences seen in
the ultraviolet for objects which do not appear remarkable in the optical. We
find that the UV/optical brightness and broad light curves are broadly
consistent with additional flux from the shock of the ejecta hitting a red
giant companion. SN~2011de is either the first external interaction of a SN Ia
discovered in the UV or an extreme example of the intrinsic UV variations in
SNe Ia.

High Energy Astrophysical Phenomena