The 43-year-old actress is currently filming Miracles from Heaven in Atlanta, and on her day off on Sunday, she and her costar, Kylie Rogers, visited Children's Healthcare of Atlanta at Scottish Rite. During her visit, Garner met a 9-year-old patient named Henry Shepherd, who has been diagnosed with Osteosarcoma, a rare form of bone cancer.
The 13 Going on 30 actress happily posed with Henry, Henry's twin sister, and Kylie, at his bedside.
Garner visited Henry for about 10 minutes as he was getting his second-to-last chemotherapy treatment, and his mother, Carrie Shepherd, described the A-list star to ET as "very down to earth, very kind, has a big heart and very genuine."
"We didn't know we were going to meet her, it was a complete surprise," she further shared. "She, like me, is a mother of three. It was an honor to meet her. She's a big celebrity but more than that, just a nice, kind and warm person."
Henry said he was "surprised" by Garner's unexpected visit, where they talked about making movies in Atlanta, and couldn't help but gush about the actress, saying "she was very nice." Henry also gave an update on his treatment, saying he "was excited about his last chemo treatment [Friday]."
The Shepherd family has set up a GiveForward page to help with Henry's medical treatments, and have raised $18,235 so far, with a goal to raise $100,000.
Henry's story definitely hits close to home when it comes to Garner's latest film, which is about a young girl suffering from a rare digestive disorder that finds herself miraculously cured after surviving a serious accident. Set to come out next year, the film is based off the book Three Miracles From Heaven by Christy Beam.
Last month, Garner and her ex, Ben Affleck, announced their split just one day after marking their 10-year wedding anniversary. Affleck is now being linked to their former nanny, 28-year-old Christine Ouzounian, who a source tells ET had only worked with the family for "a matter of months" and had joined Affleck and Garner in the Bahamas earlier this month after the couple announced they were divorcing.
The 42-year-old actor has denied the Us Weekly report that he was romantically involved with Ouzounian, his rep calling the claims "complete garbage and full of lies."
However, photos have surfaced of Ouzounian bringing Affleck champagne at his rental home in Los Angeles, though another source tells ET that Ouzounian "tipped off the paparazzi" about that rendezvous so that photos would be taken of her and Affleck together.