Iron Man actor Robert Downey Jr has visited Great Ormond Street Hospital, where he met young fans on the cancer ward.
Ahead of the European premiere of Captain America: Civil War in London on Tuesday, the film's star spent Monday afternoon visiting patients and their families and handing out Captain America goodies.
Seven-year-old Ethan Miller, who suffers from the rare blood disease ITP as well as type 1 diabetes, was "over the moon" to meet the Hollywood actor.
His father Lee said: "Ethan has been in and out of hospital a lot in the past three years. He watches the films all the time and virtually lives in his Iron Man costume.
"Ethan was over the moon to meet his hero and it has really helped to lift his spirits."
The two posed together in the hospital chapel, with Ethan wearing his Iron Man costume.
Downey said of the visit: "The highlight of the Captain America: Civil War tour has been visiting the patients, families and staff at Great Ormond Street Hospital. Their courage, strength and hope leaves me humbly inspired."
Downey has played Tony Stark - otherwise known as Iron Man - since 2008.
This is not the first time the actor has used his fame and acting skills to surprise young fans.
Last year, he visited Alex Pring, then seven years old, who was born with a partially developed right arm. Showing up in character as Tony Stark, he presented Alex with a bionic Iron Man arm.
He also had a special message for a young boy suffering from cystic fibrosis, donning a Tigger costume and posing for an Instagram photograph to cheer him up and invite him to the Captain America premiere.
Great Ormond Street Hospital is one of the world's leading children's units, treating young patients with rare, complex and life-threatening conditions.
The visit was organised by Disney officials, who have worked with the hospital's charity since 2008, raising more than £10 million for the unit's redevelopment.