Petronella Osgood (Doctor Who)

Petronella Osgood was a scientist who worked for UNIT, acting in a capacity of a personal assistant to Kate Stewart, in the early 21st century.

An admirer of the Doctor, she eventually met the Time Lord during the infiltration of UNIT by Zygon invaders, which was resolved by the Eleventh Doctor joined by his tenth and war incarnations. (TV: The Day of the Doctor)

The original Osgood and her Zygon double became indistinguishable from each other to everyone else. They refused to identify which one of them was Zygon and which was human. (TV: The Zygon Invasion) One of them was killed by Missy. (TV: in Heaven) After a Zygon rebellion was ended peacefully, the Zygon rebel leader Bonnie took on the form of Osgood to maintain the peace. Both Osgoods still refused to identify if she was the human or Zygon version but promised to identify if she was human or Zygon one day when no one would care anymore. (TV: The Zygon Inversion)

Personality:

Osgood was a "fan" of the Doctor and knew of many of his previous incarnations. She would pick iconic items (i.e. multi-coloured scarf, bow tie) from the incarnations she knew of and wore them herself (TV: The Zygon Inversion) When asked by the Twelfth Doctor if she would like to travel with him, she was so excited that she had to use her inhaler. (TV: in Heaven) Osgood would become saddened if she learned she missed a chance to see the Doctor; one of her fellow scientists even stated she would be disheartened to learn the Doctor had regenerated again after she had just started mimicking his previous self's fashion. (COMIC: The Fractures)

Osgood was also very intelligent. She alone was able to work out the reason why the Zygons smashed the statues in the Under-Gallery. (TV: The Day of the Doctor) She also surprised the Twelfth Doctor by correctly presuming that Missy was the Master regenerated into female form: UNIT kept files on all past Prime Ministers, including the Master. (TV: in Heaven) She also came up with a hypothetical plan for invading Earth by killing the Doctor by shooting him between the eyes for each regeneration, never allowing him to talk. (TV: The Zygon Inversion)

She managed to figure out whether she or her Zygon doppelganger was the real Osgood after the Tenth and Eleventh Doctors, joined by the War Doctor, jumbled their minds, making them unable to determine their own species, in an attempt to facilitate negotiation of the ultimate peace treaty. She managed to determine this as her Zygon counterpart suffered an asthma attack, motivating her to pass her asthma inhaler to the other Osgood. (TV: The Day of the Doctor)

Osgood had a sister to whom she negatively compared herself. (TV: The Day of the Doctor) Missy observed that she had little confidence in herself. Osgood was able to keep her cool, even when faced with the threat of from Missy and tried to reason her way out. (TV: in Heaven)

Where is Osgood when she becomes naked and how does it happen?