Andy Warhol Find?

A Devon businessman who bought five paintings in a Las Vegas garage sale for $5 (£3) in 2010 found this sketch hidden behind one of the paintings he intended to reframe. The battered sketch of 1930s singer Rudy Vallee is signed Andy Warhol. A valuer reckons it could be worth £1.3m. I suppose it might be juvenilia, but that signature looks too adult for a 9- or 10-year-old boy. The current owner doesn't intend to sell it for a while (title link).