Clapton recalled a period in the 1980s when he was on the road and caught in what he called a "downward spiral with drink and drugs."
Then he saw Prince's Purple Rain in a Canadian movie theater and, Clapton said, it hit him like a bolt of lightning. The musician said he went back to his hotel, amid empty beer cans, and wrote "Holy Mother."
Prince's Family & Friends Gather for Private Memorial Service at Paisley Park
Clapton wrote on Facebook that he can't believe Prince is gone.
The 57-year-old Prince was found dead Thursday in his suburban Minneapolis home, with the cause of death unknown.