(Photo: CGTN)

The painting which was found in a London flat in February, and auctioned for $1.5m (£1.2m) to an anonymous buyer, was the highest-valued work at the three-day ArtX Lagos fair, which ended on Sunday.

Tutu, by Nigeria's best-known modern artist, Ben Enwonwu, was painted in 1974 and appeared at an art show in Lagos the following year. It then disappeared until it re-surfaced in north London.

The painting is a portrait of Adetutu Ademiluyi, a grand-daughter of a traditional ruler from the Yoruba ethnic group.

It holds special significance in Nigeria as a symbol of national reconciliation after the 1967-1970 Biafran War.

The owners – who wished to remain anonymous – had called in Giles Peppiatt, an expert in modern and contemporary African art at the London auction house Bonhams, to identify their painting. He recognised Enwonwu's portrait.

“It was discovered by myself on a pretty routine valuation call to look at a work by Ben Enwonwu,” said Mr. Peppiatt.

“I didn't know what I was going to see. I turned up, and it was this amazing painting. We'd had no inkling Tutu was there. How it got there remains a bit of a mystery,” Peppiatt said.