I have been getting news alerts on this story for a few days, but I was waiting for one of the stories to actually run a picture of the portrait before I posted it. Thankfully the BBC finally came through! The portrait is a large version of a relatively well-known miniature of Thomas Wyatt the Younger, which you can see here.

From the BBC article:

A recently rediscovered painting by Hans Holbein is expected to fetch between £2m and £3m at auction.
The Portrait of Sir Thomas Wyatt the Younger, painted in about 1541, will go on sale at Sotheby’s in London in July.

Its identity is thought to have been unknown for more than 200 years, before it was confirmed earlier this year.

Full article

Other articles:

From The Telegraph

From The Independent