Apparently the singer is due to give birth in two months time – meaning she was six months pregnant when she shared the happy news.
There's been no confirmation of her due date from the 24-year-old.
However, the pregnancy may have been well advanced already in May when she was absent from the Billboard awards in America, despite winning 12 trophies.
Then when she attended the Ivor Novello awards a week later, the star wore a very loose fitting black dress that could have easily concealed a sizeable bump.
The Rolling in the Deep singer also arrived late and refused to give interviews or pose for pictures even though she's usually very friendly with the press.
A source told Heat magazine: "Adele has barely left the house in recent months, so she could keep this to herself for as long as possible.
"She stopped exercising a few months ago, and since then it's been all about the baby."
Adele made the announcement on June 30 on her blog under a post titled "I've got some news".
She wrote: "I'm delighted to announce that Simon and I are expecting our first child together.
"I wanted you to hear the news direct from me, obviously we're over the moon and very excited… Yours always, Adele."