Gwen Stefani and Blake Shelton apply for marriage license as they prepare to tie the knot

Gwen Stefani and Blake Shelton look set to tie the knot after nearly six years together. The No Doubt singer, 51, and the country star, 45, have applied for a marriage license in Oklahoma, TMZ reported Thursday. The move means the couple are likely to marry soon, as the permit is only valid for 10 …