Pregnant Meghan Markle in 'Happiest Period of Her Life' Ahead of Royal Baby's Arrival

Royal expert Katie Nicholl breaks down all the reasons behind the Duchess of Sussex's 'megawatt smile.'

Meghan Markle is seriously glowing!

The Duchess of Sussex has been stepping out with a permanent "megawatt smile" on her face lately, as royal expert Katie Nicholl so perfectly put it during a sit-down interview with ET on Wednesday. Now, we're breaking down all the reasons why Markle can't stop beaming.

The former Suits star is currently expecting her first child with husband Prince Harry, which obviously has a lot to do with her newfound happiness. "She has told friends that this is the most exciting [time], the happiest period in her life," Nicholl says. "I'm told that she is upbeat and that she is happy."

"Behind the scenes, she and Harry are really happy at the moment," Nicholl continues, adding that the two are getting ready to transition their lives away from Kensington Palace full-time. "They are super excited about the spring birth of their baby. They are very much looking forward to moving into their new home in Frogmore Cottage."

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Earlier this week, Markle reportedly revealed how far along she is in her pregnancy (six months), along with her due date (late April to early May) to a woman in the crowd in Birkenhead, England. But does the mom-to-be have any plans to announce the baby's gender?

"The couple has said that they don't know the sex of their baby," Nicholl says. "Meghan gave away a little detail that we've all been hoping to hear, that it's going to be a spring baby."

"They've decided not to find out the sex," she adds, "but according to sources who are helping with [their new home] renovations, the nursery itself is going to be very modern. Don't expect to see any baby pink or baby blue. Apparently, it's going to be a monochrome palette -- whites and grays, I'm told, will be the color theme for baby Sussex's nursery."

Hear more on how the Duke and Duchess of Sussex are preparing for the baby's arrival in the video below!