Jack Brooksbank's nana's brutal words about her grandson

Jack Brooksbank's grandmother said he was a "good egg". Photo / AP

Princess Eugenie has been praised by her fiance's grandmother for agreeing to marry her "charming" grandson — but joked he is not the "most intelligent".

The lighthearted comment by Jack Brooksbank's grandmother comes as speculation mounts about a date for the couple's wedding.

Joanna Newton, 91, told MailOnline: "I never thought he would get married to a royal. He's a charming boy and all that but not the most intelligent and I would never have thought this would happen."

The pensioner said her wine merchant grandson, 31, and his 27-year-old fiancee — who have said they will marry this autumn — had wanted to exchange vows in September but were now looking at October as their wedding month.

The couple announced their engagement with a pink sapphire ring in what will be the second of two royal wedding this year following Prince Harry and Meghan Markle in May.

With the Queen and Duke of Edinburgh traditionally spending September in Scotland at Balmoral, the month was unlikely to have been a serious contender for the wedding.

The monarch usually returns from her summer break in the second week of October, making dates around the middle of that month the likely period for the royal nuptials.

Another period for Eugenie to avoid is during Prince Harry's Invictus Games, which he and fiancee Meghan Markle are expected to attend from October 18 when they begin in Australia.

Brooksbank's grandmother described him as a "good egg" and told MailOnline: "I think it says a lot about Eugenie that it's him she wants and it's lovely."