The 17-year-old singer visited wards at the hospital where he was once treated, and performed for the youngsters.
Nicholas, from Wishaw, suffers from Long QT Syndrome, also known as Sudden Death Syndrome, and has received treatment for his condition at Yorkhill.
He performed two songs for patients, including seven-year-old Logan Rankin, left, as a way of showing his appreciation for the care he received there.
Nicholas and his family have raised around £5000 for Yorkhill Children's Charity since he was cared for at the Glasgow hospital as a child.
The teenage crooner came second in the hit talent show, narrowly missing out to Sam Bailey.
Music label RCA Records snapped up the star, who will release his debut album in March.