The legendary singer sang 'there's only one Neil Lennon' has the Northern Irishman undertook an interview with the club's official channel.
The pair had just watched James Forrest net a late winner at Celtic Park which all but confirmed the club's eighth league title in a row.
While being asked a question Lennon winks at a passing Stewart who belted out the song.
The Celtic boss said: "That's Sir Rod Stewart there, so it is. Legend that he is. Loving the shoes as well."
Stewart, a huge Celtic supporter, made himself known at the ground on Sunday with an impressive pair of Celtic shoes.
He was also filmed with his sons singing along together to Irish ballad 'Grace'.
The singer did a cover of the song after hearing it sung by Celtic fans.
He told Billboard magazine: "So I heard the Celtic supporters singing it about three years ago. I went over to Dublin and did my homework.I visited the jail (Kilmainham, now a museum) and went into the chapel where it all happened.So it means a lot to me, that one, it really does."
He claimed in 2018 that he was banned from singing it on the BBC because of its "Irish, anti-English overtones".