Williams, 38, posted the overtly emotional but typically comical news on his website, revealing that he and Field, 32, are going to be parents.
He wrote: “Hey friendlies, I’ve been keeping a secret from you all. Me and Ayda are going to be a Mummy and Daddy this year!!!!!!!!”
He added: “We had sex! It works!
“We’ve seen scans and cried… looked at babies in commercials and teared up… the nursery is already planned.
“Basically I’m in love with a little person growing in mummy’s belly… and can’t wait to be a daddy. Crying now.
“Much love, much joy. Roberto, Mum and Little Bump. xxx”
So many fans visited the site to see the announcement earlier today that it crashed under the high volume of traffic.
The pair have made it clear since their wedding, which took place in 2010 at the singer’s Los Angeles home, that they want kids.
Field told the Daily Mirror soon after that she couldn’t wait to have kids.
She jokingly added: “I hope they are not minging.
“Some people at my school had the ugliest parents, and they came out pretty. I hope ours gets all the best bits, but it’s pot luck who gets the minging ones. Hmmm, I’ll love them any way, I guess.”
Williams said last July that he didn’t mind if they had a boy or girl.
“The next time we go on tour there will be a little Williams in the dressing room,” he said.
“It’s about time. Baby girl or baby boy? I’m truly not bothered as long as we have a healthy baba.
“I can play footie with a boy, but a girl would defo be a daddy’s girl. So we would be blessed with either. Thinking about it.”