John Shearer / Invision/AP 1 / 8
John Shearer / Invision/AP 1 / 8

Robert Pattinson thrilled fans by showing up unannounced at a children's hospital in Los Angeles last week.

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The "Twilight" star stunned young patients in the Teen Lounge at the Children's Hospital Los Angeles on Aug. 16 when he arrived on a visit, which had been kept secret by hospital staff. The star sat with patients and painted picture frames, posed for pictures, and visited two young fans with cystic fibrosis who were unable to leave their rooms.

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Hospital staff member Ana Vega says, "Robert was so nervous about meeting the kids -- he didn't want to let them down -- which is a testament to how humble he is.

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"He was incredibly gracious and kind. He will probably never fully understand what a huge lift he gave to these kids today, and how it will positively impact them over the long term."