GaGa attends her sisters graduation!

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UPPER EAST SIDE — Lady Gaga returned to her Upper East Side roots Thursday afternoon to attend her sister's graduation from the Convent of the Sacred Heart, dressed in God knows what.

Wearing a see-through (yes, see-through) lacy pantsuit, broad black hat and black veil, the pop mega star was spotted outside the prestigious all-girls Catholic school she also attended.

She was checking her "Videophone." No word on whether Beyoncé was on the line.

A handful of "Paparazzi" turned up for the ritzy graduation at East 91st Street and Fifth Avenue to snap some photos as security guards whisked Gaga into a waiting black SUV.