Joanne Froggatt suffered an embarrassing moment when she met Duchess Catherine.

Joanne Froggatt

Joanne Froggatt

The 'Downton Abbey' star - who plays Anna Bates, the maid of Lady Mary (Michelle Dockery) in the period drama - accidentally made an inappropriate joke about being in Mary's bedroom while speaking to the royal.

Speaking about meeting the duchess when she visited the set one day, Joanne said: "It was a little bit neve-racking and I got a bit jittery.

"So she came over to say 'hi' afterwards, and I said, 'Hello, lovely to meet you,' and she said, 'It feels strange being in your bedroom,' because we're standing in Lady Mary's bedroom, and I said, 'Yeah not very many people get to come in Lady Mary's bedroom.'

"And then I thought, 'Oh god, what have I just said?' "

Fortunately, the duchess didn't appear to notice the 35-year-old star's faux pas and Joanne decided to remain quiet about it rather than try to apologise for her quip.

The actress admits she felt very nervous acting in scenes in front of the royal beauty.

Speaking on US talk show 'Conan', she explained: "You're just getting more and more nervous."

"We're doing this scene and she's very beautiful, lovely. She has this amazing aura when she walks in the room, before we actually said 'hello' we had to act right in front of her."